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9L0-403 Mac OS X uphold Essentials 10.6

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9L0-403 exam Dumps Source : Mac OS X uphold Essentials 10.6

Test Code : 9L0-403
Test cognomen : Mac OS X uphold Essentials 10.6
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Apple Apple Mac OS X

Apple Brings Mac Mini returned From the lifeless | actual Questions and Pass4sure dumps

Apple’s limited computing device pc is not any longer just a punchline. today the company took the wraps off a revamped Mac Mini, replacing its underpowered materials with new, eighth technology Intel quad- and 6-core processors options, up to 64GB of memory, as much as a 2TB SSD, a T2 protection chip, 10GB ethernet, and 4 Thunderbolt three ports. With the enhancements, Apple is bumping its longstanding $500 climb expense as much as $800—however you won’t locate face-melting specs devoid of paying even more.

sure, you’ll nonetheless need to bring your personal reveal, keyboard, and mouse. And positive that you could, uh, accumulate it in space gray now. At $800, the bottom mannequin will approach with 8GB of memory, a three.6GHz quad-core i3 processor, and 128GB of SSD storage.

The Mini was firstly designed to win over fresh converts to OS X (now macOS) with the first sub-$500 Mac. ultimate revamped eons in the past, in October 2014, it became a husk for outdated guts that nobody, fully nobody in their commandeer irony had any commerce recommending to a family member. by pass of the conclusion of its run, the newest incarnation appeared designed to thrust consumers during this budget faraway from Apple, against improved offers from corporations fondness Dell and HP.

Apple is billing the fresh Mini as “5 times faster” typical with “60 percent faster pictures.” It’ll be attainable on November 7.

Apple publicizes free OS X Mavericks free up, fresh iPads, Mac pro | actual Questions and Pass4sure dumps

At Apple’s “a worthy deal to cover” special experience nowadays, the enterprise paraded out an hour and a half’s value of latest products and updates, including the free up of OS X Mavericks, the fresh iPad Air and iPad Mini, Mac pro, updated 13 and 15-inch MacBooks, and an up-to-date suite of iLife apps.

OS X MavericksThe working gadget is free, and it’s available today. Apple senior vice president of application engineering Craig Federighi prefaced the release with, “This one is a doozy.”

obtainable with a single-step better from Snow Leopard, Lion, Mountain Lion or any MacBook dating again to 2007, Mavericks has a slew of recent features. Its fresh compressed remembrance feature allocates images reminiscence based on usage to optimize performance. The capability permits 6GB of facts to hale into 4GB of gadget RAM.

(Beta feedback and an entire record of elements: users poke around OS X ‘Mavericks’)

Mavericks’ OpenCL uses remembrance sharing to circulation tasks running on the CPU to the GPU, taking skills of the GPU’s superior computing vigour to comprehensive projects 1.8x sooner, and 2x sooner for picture initiatives.

a fresh finder window enables initiatives and files to be labeled with dissimilar tags for convenient search and firm. click the title bar of any document so as to add one or extra tags, or select a tag from a listing.

In Safari, Mavericks introduces more suitable notifications, enabling users to respond within the pop-up bubble devoid of leaving an software. It additionally adds web site notifications when fresh content is posted. the brand fresh Safari properly websites view generates a feed of shared links from followed clients on sociable networks equivalent to LinkedIn and Twitter.

There’s besides a brand fresh reader view, permitting consumer-accelerated scrolling at once from one article to the subsequent devoid of clicking out.

a pass to Revisit each version of Mac OS X out of your Browser | actual Questions and Pass4sure dumps

The Aqua GUI in Apple’s working methods has gone through a fabulous evolution due to the fact March of 2000, when it discovered its approach into OS X 10.0, and besides you could be stunned at simply how distinctive every thing looks now. because of the newly launched Aqua Screenshot Library, that you could revisit every version of OS X (and macOS) through the years and deem about the gradual evolution of Apple’s working equipment—all from your browser.

The expansive gallery is the latest travail by pass of 512 Pixels, an online library that makes an attempt to hold tabs on every things Apple (including the Mac’s many wallpapers). The Aqua Screenshot Library, as creator Stephen Hackett notes, offers a complete glance at the inheritance of Apple’s working techniques, which covers its start to from bulkier CRTs to compact, LED-backlit shows; Apple’s a lot of font adjustments over the years; and Apple’s circulation from disc-based mostly working programs to (free) digital downloads.

Let’s rob a glance at some of those major Mac milestones.

Mac OS X 10.0 (“Cheetah”)

March 24, 2001, marked the primary actual release of the Mac OS X operating system, following a public beta the year before. Hackett notes that its 128MB reminiscence requirement changed into “more than most Mac users had of their programs at the time.” This result in many complaints about the OS’s gradual performance and tall useful resource demand. The Cheetah interface retained the pin-striped menu and window design from the beta, but it started the tom cat-primarily based naming style which would final up to edition 10.8, “Mountain Lion.”

Mac OS X Leopard (10.5)

The closing months of 2007 brought some great changes to OS X. The unlock of Leopard noticed Aqua rob on a tons greater streamlined appear, with every windows now defaulting to a single, basic gray design, as neatly as the debut of a redesigned Finder tool. previous to this, different apps—and diverse types of OS X—had assorted UI designs (for better or worse). With Leopard’s release, OS X every started to appear more uniform. most significantly, it became the first version to include those rad, space-based backgrounds.

OS X Mountain Lion (10.eight)

Mountain Lion became the first edition of OS X to achieve after Steve Jobs’ loss of life, and it focused on aligning Mac computers with the late CEO’s other foremost contribution to the tech trade: the iPhone. The 2011 OS X update, Mac OS X Lion (10.7), kicked off Apple’s merging of iOS aesthetics into OS X, and the commerce doubled down with Mountain Lion. apparatus and purposes were renamed after iOS aspects, and Apple introduced some small visual and input changes to bridge both operating techniques even nearer together—in vogue, at the least.

OS X Mavericks (10.9)

Mavericks became a massive company pivot for Apple, as it became the primary version of the OS the enterprise launched at no cost, offered to users as an upgrade by the employ of the App store in October 2013. Apple hasn’t gone again to paid operating methods when you regard that—fortunately. Mavericks became besides the first version of OS X to do employ of non-tom cat nomenclature. It additionally ditched the galactic history theme for California landscapes, which they can every disagree changed into an well-known blunder. appropriate?

macOS Sierra (10.12)

version 10.12 of Apple’s working system for the Mac is most is excellent for its massive rebranding. Apple dropped the “OS X” identify totally during this release, instead calling its operating device “macOS” to align it the company’s working techniques on different systems: iOS, watchOS, and tvOS. 

browsing the Aqua Screenshot Library is a fun approach to descry simply how far macOS has come, above every to peer how Apple’s design priorities change between the primary releases. although, the Aqua Screenshot gallery is just one of 512 Pixels’ many projects to check out. do inevitable to poke across the different Apple-themed collections Hackett has assembled through the years, too, together with the impressive 512 Pixels YouTube channel.

9L0-403 Mac OS X uphold Essentials 10.6

Study lead Prepared by Apple Dumps Experts 9L0-403 Dumps and actual Questions

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9L0-403 exam Dumps Source : Mac OS X uphold Essentials 10.6

Test Code : 9L0-403
Test cognomen : Mac OS X uphold Essentials 10.6
Vendor cognomen : Apple
brain dumps : 71 actual Questions

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Apple signals finish to Mac OS X 10.6 Snow Leopard uphold | actual questions and Pass4sure dumps

“Apple has apparently decided to cancel uphold for OS X Snow Leopard, the 2009 operating system that has resisted retirement for more than a year,” Gregg Keizer reports for Computerworld.

“On Monday, Apple did not update Safari 5.1 when it patched the later Safari 6 and 7 for newer editions of OS X, including 2011’s Lion, 2012’s Mountain Lion and this year’s Mavericks. Safari 5.1, which was last updated in September to version 5.1.10, is the most-current Apple browser for Snow Leopard,” Keizer reports. “Historically, Apple has patched Safari longer than the supporting operating system, so when the Cupertino, Calif. company calls its quits for the browser, it’s already decided to retire the pertinent OS.”

“Apple’s uphold for even newer editions of OS X, including 2011’s Lion and last year’s Mountain Lion, has besides approach into question: In a very unusual move, the Cupertino, Calif. company declined to update either of those operating systems in October, when it released Mavericks with patches for more than 50 security vulnerabilities,” Keizer reports. “It’s certainly feasible that Apple has already pulled the plug on Lion and Mountain Lion, what with the two-month stretch without a badge of fixes for the bugs patched in Mavericks. Because Apple made Mavericks a free upgrade from Snow Leopard, Lion and Mountain Lion, Apple could rationalize the dropping of uphold for the latter two.”

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Discovering Mac OS X 10.6 Snow Leopard | actual questions and Pass4sure dumps

See what Apple gives you in this Mac OS X update for just $29. You won't descry expansive interface changes, but there has been a lot of travail done under the hood. Eric Geier discusses most of the performance enhancements and fresh features.

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Apple released an update to the Mac OS X operating system (OS), Snow Leopard, at the finish of August. This makes it version 10.6. Although it might not relish as many visual changes as Windows 7 does from Vista, it does relish many notable enhancements and additions. The first thing you'll probably notice is the price: It's only $29 to upgrade from version 10.5.

Since Tiger, Apple has been adding more and more 64-bit support. The Mac OS X kernel in Snow Leopard and most of the OS applications relish been rebuilt to rush at 64-bit in addition to 32-bit. However, this excludes iTunes, Front Row, Grapher, and DVD Player applications. Plus perquisite now only a select number of Apple computers are compatible with every the added support.

If you aren't a power user and relish a typical 32-bit processor, this doesn't assist you out. But if you carry out invest in a more powerful system, Mac OS X is ready more than ever.

Running a 64-bit processor means it can process bigger chunks of data more quickly, giving you a faster, higher-performing computer.

Mac OS X 10.6 Snow Leopard: the Ars Technica review | actual questions and Pass4sure dumps

Mac OS X 10.6 Snow Leopard: the Ars Technica review reader comments Share this story
  • Mac OS X 10.4 Tiger: 150+  fresh featuresMac OS X 10.4 Tiger: 150+ fresh features

    In June of 2004, during the WWDC keynote address, Steve Jobs revealed Mac OS X 10.4 Tiger to developers and the public for the first time. When the finished product arrived in April of 2005, Tiger was the biggest, most important, most feature-packed release in the history of Mac OS X by a wide margin. Apple's marketing drive reflected this, touting "over 150 fresh features."

    All those fresh features took time. Since its introduction in 2001, there had been at least one major release of Mac OS X each year. Tiger took over a year and a half to arrive. At the time, it definitely seemed worth the wait. Tiger was a hit with users and developers. Apple took the lesson to heart and quickly set expectations for the next major release of Mac OS X, Leopard. Through various channels, Apple communicated its purpose to paddle from a 12-month to an 18-month release cycle for Mac OS X. Leopard was officially scheduled for "spring 2007."

    As the date approached, Apple's marketing machine trod a predictable path.

    Steve Jobs at WWDC 2007, touting 300  fresh features in Mac OS X 10.5 LeopardSteve Jobs at WWDC 2007, touting 300 fresh features in Mac OS X 10.5 Leopard

    Apple even went so far as to list every 300 fresh features on its website. As it turns out, "spring" was a bit optimistic. Leopard actually shipped at the finish of October 2007, nearly two and a half years after Tiger. Did Leopard really relish twice as many fresh features as Tiger? That's debatable. What's inevitable is that Leopard included a solid crop of fresh features and technologies, many of which they now rob for granted. (For example, relish you had a discussion with a potential Mac user since the release of Leopard without mentioning Time Machine? I certainly haven't.)

    Mac OS X appeared to be maturing. The progression was clear: longer release cycles, more features. What would Mac OS X 10.6 be like? Would it arrive three and a half years after Leopard? Would it and include 500 fresh features? A thousand?

    At WWDC 2009, Bertrand Serlet announced a paddle that he described as "unprecedented" in the PC industry.

    Mac OS X 10.6 - Read Bertrand's lips: No  fresh Features!Mac OS X 10.6 - Read Bertrand's lips: No fresh Features!

    That's right, the next major release of Mac OS X would relish no fresh features. The product cognomen reflected this: "Snow Leopard." Mac OS X 10.6 would merely be a variant of Leopard. Better, faster, more refined, more... uh... snowy.

    This was a risky strategy for Apple. After the rapid-fire updates of 10.1, 10.2, and 10.3 followed by the riot of fresh features and APIs in 10.4 and 10.5, could Apple really accumulate away with calling a "time out?" I imagine Bertrand was really sweating this announcement up on the stage at WWDC in front of a live audience of Mac developers. Their reaction? impulsive applause. There were even a few hoots and whistles.

    Many of these same developers applauded the "150+ fresh features" in Tiger and the "300 fresh features" in Leopard at past WWDCs. Now they were applauding zero fresh features for Snow Leopard? What explains this?

    It probably helps to know that the "0 fresh Features" skid came at the finish of an hour-long presentation detailing the major fresh APIs and technologies in Snow Leopard. It was besides quickly followed by a back-pedaling ("well, there is one fresh feature...") skid describing the addition of Microsoft Exchange support. In isolation, "no fresh features" may appear to imply stagnation. In context, however, it served as a developer-friendly affirmation.

    The overall message from Apple to developers was something fondness this: "We're adding a ton of fresh things to Mac OS X that will assist you write better applications and do your existing code rush faster, and we're going to do positive that every this fresh stuff is rock-solid and as bug-free as possible. We're not going to overextend ourselves adding a raft of fresh customer-facing, marketing-friendly features. Instead, we're going to concentrate 100% on the things that influence you, the developers."

    But if Snow Leopard is a adore missive to developers, is it a Dear John missive to users? You know, those people that the marketing department might so crudely refer to as "customers." What's in it for them? Believe it or not, the sales pitch to users is actually quite similar. As exhausting as it has been for developers to maintain up with Apple's seemingly never-ending stream of fresh APIs, it can be just as taxing for customers to sojourn on top of Mac OS X's features. Exposé, a fresh Finder, Spotlight, a fresh Dock, Time Machine, a fresh Finder again, a fresh iLife and iWork almost every year, and on and on. And as much as developers dislike bugs in Apple's APIs, users who experience those bugs as application crashes relish just as much reason to be annoyed.

    Enter Snow Leopard: the release where they every accumulate a fracture from the new-features/new-bugs treadmill of Mac OS X development. That's the pitch.

    Uncomfortable realities

    But wait a second, didn't I just mention an "hour-long presentation" about Snow Leopard featuring "major fresh APIs and technologies?" When speaking to developers, Apple's message of "no fresh features" is another pass of adage "no fresh bugs." Snow Leopard is putative to fix mature bugs without introducing fresh ones. But nothing says "new bugs, coming perquisite up" quite fondness major fresh APIs. So which is it?

    Similarly, for users, "no fresh features" connotes stability and reliability. But if Snow Leopard includes enough changes to the core OS to fill an hour-long overview session at WWDC more than a year before its release, can Apple really do noble on this promise? Or will users finish up with every the disadvantages of a feature-packed release fondness Tiger or Leopard—the inevitable 10.x.0 bugs, the unfamiliar, untried fresh functionality—but without any of the actual fresh features?

    Yes, it's enough to do one quite cynical about Apple's actual motivations. To sling some more fuel on the fire, relish a glance at the Mac OS X release timeline below. Next to each release, I've included a list of its most significant features.

    Mac OS X release timelineMac OS X release timeline

    That curve is taking on a decidedly droopy shape, as if it's being weighed down by the ever-increasing number of fresh features. (The releases are distributed uniformly on the Y axis.) Maybe you deem it's reasonable for the time between releases to stretch out as each one brings a heavier load of goodies than the last, but maintain in irony the rational consequence of such a curve over the longhorn haul.

    And yeah, there's a limited upwards kick at the finish for 10.6, but remember, this is putative to be the "no fresh features" release. Version 10.1 had a similar no-frills focus but took a heck of a lot less time to arrive.

    Looking at this graph, it's arduous not to miracle if there's something siphoning resources from the Mac OS X development effort. Maybe, say, some project that's in the first two or three major releases of its life, still in that steep, early section of its own timeline graph. Yes, I'm talking about the iPhone, specifically iPhone OS. The iPhone commerce has exploded onto Apple's poise sheets fondness no other product before, even the iPod. It's besides accruing developers at an alarming rate.

    It's not a stretch to imagine that many of the artists and developers who piled on the user-visible features in Mac OS X 10.4 and 10.5 relish been reassigned to iPhone OS (temporarily or otherwise). After all, Mac OS X and iPhone OS partake the same core operating system, the same language for GUI development, and many of the same APIs. Some workforce migration seems inevitable.

    And let's not forget the "Mac OS X" technologies that they later learned were developed for the iPhone and just happened to be announced for the Mac first (because the iPhone was still a secret), fondness Core Animation and code signing. Such cabal theories certainly aren't helped by WWDC keynote snubs and other indignities suffered by Mac OS X and the Mac in general since the iPhone arrived on the scene. And so, on top of everything else, Snow Leopard is tasked with restoring some luster to Mac OS X.

    Got every that? A nearly two-year development cycle, but no fresh features. Major fresh frameworks for developers, but few fresh bugs. Significant changes to the core OS, but more reliability. And a franchise rejuvenation with few user-visible changes.

    It's enough to spin a leopard white.

    The price of entry

    Snow Leopard's opening overture to consumers is its price: $29 for those upgrading from Leopard. The debut release of Mac OS X 10.0 and the last four major releases relish every been $129, with no special pricing for upgrades. After eight years of this kindly of fiscal disciplining, Leopard users may well be tempted to cease reading perquisite now and just paddle pick up a copy. Snow Leopard's upgrade price is well under the impulse purchase threshold for many people. Twenty-nine dollars plus some minimal even of faith in Apple's ability to better the OS with each release, and boom, instant purchase.

    Still here? Good, because there's something else you need to know about Snow Leopard. It's an overture of a different sort, less of a come-on and more of a spur. Snow Leopard will only rush on Macs with Intel CPUs. Sorry (again), PowerPC fans, but this is the finish of the line for you. The transition to Intel was announced over four years ago, and the last fresh PowerPC Mac was released in October 2005. It's time.

    But if Snow Leopard is meant to prod the PowerPC holdouts into the Intel age, its "no fresh features" stance (and the accompanying lack of added visual flair) is working against it. For those running Leopard on a PowerPC-based Mac, there's precious limited in Snow Leopard to assist thrust them over the (likely) four-digit price wall of a fresh Mac. For PowerPC Mac owners, the threshold for a fresh Mac purchase remains mostly unchanged. When their mature Mac breaks or seems too slow, they'll paddle out and buy a fresh one, and it'll approach with Snow Leopard pre-installed.

    If Snow Leopard does finish up motivating fresh Mac purchases by PowerPC owners, it will probably be the result of resignation rather than inspiration. An Intel-only Snow Leopard is most significant for what it isn't: a further extension of PowerPC life uphold on the Mac platform.

    The final inquisitive group is owners of Intel-based Macs that are still running Mac OS X 10.4 Tiger. Apple shipped Intel Macs with Tiger installed for a limited over one year and nine months. Owners of these machines who never upgraded to Leopard are not eligible for the $29 upgrade to Snow Leopard. They're besides apparently not eligible to purchase Snow Leopard for the traditional $129 price. Here's what Apple has to squawk about Snow Leopard's pricing (emphasis added).

    Mac OS X version 10.6 Snow Leopard will be available as an upgrade to Mac OS X version 10.5 Leopard in September 2009 [...] The Snow Leopard solitary user license will be available for a suggested retail price of $29 (US) and the Snow Leopard Family Pack, a solitary household, five-user license, will be available for a suggested price of $49 (US). For Tiger® users with an Intel-based Mac, the Mac Box Set includes Mac OS X Snow Leopard, iLife® '09 and iWork® '09 and will be available for a suggested price of $169 (US) and a Family Pack is available for a suggested price of $229 (US).

    Ignoring the family packs for a moment, this means that Snow Leopard will either be free with your fresh Mac, $29 if you're already running Leopard, or $169 if you relish an Intel Mac running Tiger. People upgrading from Tiger will accumulate the latest version of iLife and iWork in the contract (if that's the commandeer term), whether they want them or not. It positive seems fondness there's an obvious residence in this lineup for a $129 offering of Snow Leopard on its own. Then again, perhaps it every comes down to how, exactly, Apple enforces the $29 Snow Leopard upgrade policy.

    (As an aside to non-Mac users, note that the non-server version of Mac OS X has no per-user serial number and no activation scheme of any kind, and never has. "Registration" with Apple during the Mac OS X install process is entirely optional and is only used to collect demographic information. Failing to register (or entering entirely bogus registration information) has no upshot on your ability to rush the OS. This is considered a genuine edge of Mac OS X, but it besides means that Apple has no accountable record of who, exactly, is a "legitimate" owner of Leopard.)

    One possibility was that the $29 Snow Leopard upgrade DVD would only install on top of an existing installation of Leopard. Apple has done this type of thing before, and it bypasses any proof-of-purchase annoyances. It would, however, interject a fresh problem. In the event of a arduous drive failure or simple conclusion to reinstall from scratch, owners of the $29 Snow Leopard upgrade would be forced to first install Leopard and then install Snow Leopard on top of it, perhaps more than doubling the installation time—and quintupling the annoyance.

    Given Apple's history in this area, no one should relish been surprised to find out that Apple chose the much simpler option: the $29 "upgrade" DVD of Snow Leopard will, in fact, install on any supported Mac, whether or not it has Leopard installed. It will even install onto an entirely vacant arduous drive.

    To be clear, installing the $29 upgrade to Snow Leopard on a system not already running a properly licensed copy of Leopard is a violation of the end-user license agreement that comes with the product. But Apple's conclusion is a refreshing change: rewarding honest people with a hassle-free product rather than trying to chastise deceitful people by treating everyone fondness a criminal. This "honor system" upgrade enforcement policy partially explains the expansive jump to $169 for the Mac Box Set, which ends up re-framed as an honest person's pass to accumulate iLife and iWork at their accustomed prices, plus Snow Leopard for $11 more.

    And yes, speaking of installing, let's finally accumulate on with it.


    Apple claims that Snow Leopard's installation process is "up to 45% faster." Installation times vary wildly depending on the speed, contents, and fragmentation of the target disk, the hasten of the optical drive, and so on. Installation besides only happens once, and it's not really an inquisitive process unless something goes terribly wrong. Still, if Apple's going to do such a claim, it's worth checking out.

    To eliminate as many variables as possible, I installed both Leopard and Snow Leopard from one arduous disk onto another (empty) one. It should be famous that this change negates some of Snow Leopard's most well-known installation optimizations, which are focused on reducing random data access from the optical disc.

    Even with this disadvantage, the Snow Leopard installation took about 20% less time than the Leopard installation. That's well short of Apple's "up to 45%" claim, but descry above (and don't forget the "up to" weasel words). Both versions installed in less than 30 minutes.

    What is striking about Snow Leopard's installation is how quickly the initial Spotlight indexing process completed. Here, Snow Leopard was 74% faster in my testing. Again, the times are small (5:49 vs. 3:20) and again, fresh installations on vacant disks are not the norm. But the shorter wait for Spotlight indexing is worth noting because it's the first indication most users will accumulate that Snow Leopard means commerce when it comes to performance.

    Another notable thing about installation is what's not installed by default: Rosetta, the facility that allows PowerPC binaries to rush on Intel Macs. Okay Apple, they accumulate it. PowerPC is a stiff, bereft of life. It rests in peace. It's rung down the curtain and joined the choir invisible. As far as Apple is concerned, PowerPC is an ex-ISA.

    But not installing Rosetta by default? That seems a limited harsh, even foolhardy. What's going to occur when every those users upgrade to Snow Leopard and then double-click what they've probably long since forgotten is a PowerPC application? Perhaps surprisingly, this is what happens:

    Rosetta: auto-installed for your convenienceRosetta: auto-installed for your convenience

    That's what I saw when I tried to launch Disk Inventory X on Snow Leopard, an application that, yes, I had long since forgotten was PowerPC-only. After I clicked the "Install" button, I actually expected to be prompted to insert the installer DVD. Instead, Snow Leopard reached out over the network, pulled down Rosetta from an Apple server, and installed it.

    Rosetta auto-install

    No reboot was required, and Disk Inventory X launched successfully after the Rosetta installation completed. Mac OS X has not historically made much employ of the install-on-demand approach to system software components, but the facility used to install Rosetta appears quite robust. Upon clicking "Install," an XML property list containing a vast catalog of available Mac OS X packages was downloaded. Snow Leopard uses the same facility to download and install printer drivers on demand, saving another trip to the installer DVD. I hope this technique gains even wider employ in the future.

    Installation footprint

    Rosetta aside, Snow Leopard simply puts fewer bits on your disk. Apple claims it "takes up less than half the disk space of the previous version," and that's no lie. A clean, default install (including fully-generated Spotlight indexes) is 16.8 GB for Leopard and 5.9 GB for Snow Leopard. (Incidentally, these numbers are both powers-of-two measurements; descry sidebar.)

    A gigabyte by any other name

    Snow Leopard has another trick up its sleeve when it comes to disk usage. The Snow Leopard Finder considers 1 GB to be equal to 109 (1,000,000,000) bytes, whereas the Leopard Finder—and, it should be noted, every version of the Finder before it—equates 1 GB to 230 (1,073,741,824) bytes. This has the upshot of making your arduous disk suddenly appear larger after installing Snow Leopard. For example, my "1 TB" arduous drive shows up in the Leopard Finder as having a capacity of 931.19 GB. In Snow Leopard, it's 999.86 GB. As you might relish guessed, arduous disk manufacturers employ the powers-of-ten system. It's every quite a mess, really. Though I approach down pretty firmly on the powers-of-two side of the fence, I can't guilt Apple too much for wanting to match up nicely with the long-established (but still dumb, irony you) arduous disk vendors' capacity measurement standard.

    Snow Leopard has several weight loss secrets. The first is obvious: no PowerPC uphold means no PowerPC code in executables. Recall the maximum feasible binary payload in a Leopard executable: 32-bit PowerPC, 64-bit PowerPC, x86, and x86_64. Now cross half of those architectures off the list. Granted, very few applications in Leopard included 64-bit code of any kind, but it's a 50% reduction in size for executables no matter how you slice it.

    Of course, not every the files in the operating system are executables. There are data files, images, audio files, even a limited video. But most of those non-executable files relish one thing in common: they're usually stored in compressed file formats. Images are PNGs or JPEGs, audio is AAC, video is MPEG-4, even preference files and other property lists now default to a compact binary format rather than XML.

    In Snow Leopard, other kinds of files climb on board the compression bandwagon. To give just one example, ninety-seven percent of the executable files in Snow Leopard are compressed. How compressed? Let's look:

    % cd Applications/ % ls -l Mail -rwxr-xr-x@ 1 root wheel 0 Jun 18 19:35 Mail

    Boy, that's, uh, pretty small, huh? Is this really an executable or what? Let's check their assumptions.

    % file Applications/ Applications/ empty

    Yikes! What's going on here? Well, what I didn't divulge you is that the commands shown above were rush from a Leopard system looking at a Snow Leopard disk. In fact, every compressed Snow Leopard files appear to accommodate zero bytes when viewed from a pre-Snow Leopard version of Mac OS X. (They glance and act perfectly customary when booted into Snow Leopard, of course.)

    So, where's the data? The limited "@" at the finish of the permissions string in the ls output above (a feature introduced in Leopard) provides a clue. Though the Mail executable has a zero file size, it does relish some extended attributes:

    % xattr -l Applications/ 0000 00 00 01 00 00 2C F5 F2 00 2C F4 F2 00 00 00 32 .....,...,.....2 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ (184,159 lines snipped) 2CF610 63 6D 70 66 00 00 00 0A 00 01 FF FF 00 00 00 00 cmpf............ 2CF620 00 00 00 00 .... 0000 66 70 6D 63 04 00 00 00 A0 82 72 00 00 00 00 00 fpmc......r.....

    Ah, there's every the data. But wait, it's in the resource fork? Weren't those deprecated about eight years ago? Indeed they were. What you're witnessing here is yet another addition to Apple's favorite file system hobbyhorse, HFS+.

    At the dawn of Mac OS X, Apple added journaling, symbolic links, and arduous links. In Tiger, extended attributes and access control lists were incorporated. In Leopard, HFS+ gained uphold for arduous links to directories. In Snow Leopard, HFS+ learns another fresh trick: per-file compression.

    The presence of the attribute is the first hint that this file is compressed. This attribute is actually hidden from the xattr command when booted into Snow Leopard. But from a Leopard system, which has no erudition of its special significance, it shows up as unpretentious as day.

    Even more information is revealed with the assist of Mac OS X Internals guru Amit Singh's hfsdebug program, which has quietly been updated for Snow Leopard.

    % hfsdebug /Applications/ ... compression magic = cmpf compression type = 4 (resource fork has compressed data) uncompressed size = 7500336 bytes

    And positive enough, as they saw, the resource fork does indeed accommodate the compressed data. Still, why the resource fork? It's every piece of Apple's usual, clever backward-compatibility gymnastics. A recent sample is the pass that arduous links to directories exhibit up—and function—as aliases when viewed from a pre-Leopard version of Mac OS X.

    In the case of a HFS+ compression, Apple was (understandably) unable to do pre-Snow Leopard systems read and interpret the compressed data, which is stored in ways that did not exist at the time those earlier operating systems were written. But rather than letting applications (and users) running on pre-10.6 systems choke on—or worse, deprave through modification—the unexpectedly compressed file contents, Apple has chosen to cover the compressed data instead.

    And where can the complete contents of a potentially great file be hidden in such a pass that pre-Snow Leopard systems can still copy that file without the loss of data? Why, in the resource fork, of course. The Finder has always correctly preserved Mac-specific metadata and both the resource and data forks when poignant or duplicating files. In Leopard, even the lowly cp and rsync commands will carry out the same. So while it may be a limited bit spooky to descry every those "empty" 0 KB files when looking at a Snow Leopard disk from a pre-Snow Leopard OS, the desultory of data loss is small, even if you paddle or copy one of the files.

    The resource fork isn't the only residence where Apple has decided to smuggle compressed data. For smaller files, hfsdebug shows the following:

    % hfsdebug /etc/asl.conf ... compression magic = cmpf compression type = 3 (xattr has compressed data) uncompressed size = 860 bytes

    Here, the data is small enough to be stored entirely within an extended attribute, albeit in compressed form. And then, the final frontier:

    % hfsdebug /Volumes/Snow Time/Applications/ ... compression magic = cmpf compression type = 3 (xattr has inline data) uncompressed size = 8 bytes

    That's right, an entire file's contents stored uncompressed in an extended attribute. In the case of a benchmark PkgInfo file fondness this one, those contents are the four-byte classic Mac OS type and creator codes.

    % xattr -l Applications/ 0000 66 70 6D 63 03 00 00 00 08 00 00 00 00 00 00 00 fpmc............ 0010 FF 41 50 50 4C 65 6D 61 6C .APPLemal

    There's still the same "fpmc..." preamble seen in every the earlier examples of the attribute, but at the finish of the value, the expected data appears as unpretentious as day: type code "APPL" (application) and creator code "emal" (for the Mail application—cute, as per classic Mac OS tradition).

    You may be wondering, if this is every about data compression, how does storing eight uncompressed bytes plus a 17-byte preamble in an extended attribute save any disk space? The acknowledge to that lies in how HFS+ allocates disk space. When storing information in a data or resource fork, HFS+ allocates space in multiples of the file system's allocation secrete size (4 KB, by default). So those eight bytes will rob up a minimum of 4,096 bytes if stored in the traditional way. When allocating disk space for extended attributes, however, the allocation secrete size is not a factor; the data is packed in much more tightly. In the end, the actual space saved by storing those 25 bytes of data in an extended attribute is over 4,000 bytes.

    But compression isn't just about saving disk space. It's besides a classic sample of trading CPU cycles for decreased I/O latency and bandwidth. Over the past few decades, CPU performance has gotten better (and computing resources more plentiful—more on that later) at a much faster rate than disk performance has increased. Modern arduous disk quest times and rotational delays are still measured in milliseconds. In one millisecond, a 2 GHz CPU goes through two million cycles. And then, of course, there's still the actual data transfer time to consider.

    Granted, several levels of caching throughout the OS and hardware travail mightily to cover these delays. But those bits relish to approach off the disk at some point to fill those caches. Compression means that fewer bits relish to be transferred. Given the almost comical glut of CPU resources on a modern multi-core Mac under customary use, the total time needed to transfer a compressed payload from the disk and employ the CPU to decompress its contents into remembrance will still usually be far less than the time it'd rob to transfer the data in uncompressed form.

    That explains the potential performance benefits of transferring less data, but the employ of extended attributes to store file contents can actually do things faster, as well. It every has to carry out with data locality.

    If there's one thing that slows down a arduous disk more than transferring a great amount of data, it's poignant its heads from one piece of the disk to another. Every paddle means time for the head to start moving, then stop, then ensure that it's correctly positioned over the desired location, then wait for the spinning disk to save the desired bits beneath it. These are every real, physical, poignant parts, and it's astounding that they carry out their dance as quickly and efficiently as they do, but physics has its limits. These motions are the actual performance killers for rotational storage fondness arduous disks.

    The HFS+ volume format stores every its information about files—metadata—in two primary locations on disk: the Catalog File, which stores file dates, permissions, ownership, and a host of other things, and the Attributes File, which stores "named forks."

    Extended attributes in HFS+ are implemented as named forks in the Attributes File. But unlike resource forks, which can be very great (up to the maximum file size supported by the file system), extended attributes in HFS+ are stored "inline" in the Attributes File. In practice, this means a circumscribe of about 128 bytes per attribute. But it besides means that the disk head doesn't need to rob a trip to another piece of the disk to accumulate the actual data.

    As you can imagine, the disk blocks that do up the Catalog and Attributes files are frequently accessed, and therefore more likely than most to be in a cache somewhere. every of this conspires to do the complete storage of a file, including both its metadata in its data, within the B-tree-structured Catalog and Attributes files an overall performance win. Even an eight-byte payload that balloons to 25 bytes is not a concern, as long as it's still less than the allocation secrete size for customary data storage, and as long as it every fits within a B-tree node in the Attributes File that the OS has to read in its entirety anyway.

    There are other significant contributions to Snow Leopard's reduced disk footprint (e.g., the removal of unnecessary localizations and "designable.nib" files) but HFS+ compression is by far the most technically interesting.

    Installer intelligence

    Apple makes two other inquisitive promises about the installation process:

    Snow Leopard checks your applications to do positive they're compatible and sets aside any programs known to be incompatible. In case a power outage interrupts your installation, it can start again without losing any data.

    The setting aside of "known incompatible" applications is undoubtedly a response to the "blue screen" problems some users encountered when upgrading from Tiger to Leopard two years ago, which was caused by the presence of incompatible—and some would squawk "illicit"—third-party system extensions. I relish a decidedly pragmatic view of such software, and I'm cheerful to descry Apple taking a similarly practical approach to minimizing its impact on users.

    Apple can't be expected to detect and disable every potentially incompatible software, of course. I suspect only the most Popular or highest profile risky software is detected. If you're a developer, this installer feature may be a noble pass to find out if you're on Apple's sh*t list.

    As for continuing an installation after a power failure, I didn't relish the guts to test this feature. (I besides relish a UPS.) For long-running processes fondness installation, this kindly of added robustness is welcome, especially on battery-powered devices fondness laptops.

    I mention these two details of the installation process mostly because they highlight the kinds of things that are feasible when developers at Apple are given time to polish their respective components of the OS. You might deem that the installer team would be hard-pressed to approach up with enough to carry out during a nearly two-year development cycle. That's clearly not the case, and customers will gather the benefits.

    Snow Leopard's fresh looks

    I've long yearned for Apple to do a immaculate break, at least visually, from Mac OS X's Aqua past. Alas, I will be waiting a bit longer, because Snow Leopard ushers in no such revolution. And yet here I am, beneath a familiar-looking section heading that seems to betoken otherwise. The veracity is, Snow Leopard actually changes the appearance of nearly every pixel on your screen—but not in the pass you might imagine.

    Since the dawn of color on the Macintosh, the operating system has used a default output gamma correction value of 1.8. Meanwhile, Windows—aka the rest of the world—has used a value of 2.2. Though this may not appear significant to anyone but professional graphics artists, the dissimilarity is usually evident to even a casual observer when viewing the same image on both kinds of displays side by side.

    Though Mac users will probably instinctively prefer the 1.8 gamma image that they're used to, Apple has decided that this historical dissimilarity is more inconvenience than it's worth. The default output gamma correction value in Snow Leopard is now 2.2, just fondness everyone else. Done and done.

    If they notice at all, users will likely experience this change as a sentiment that the Snow Leopard user interface has a bit more contrast than Leopard's. This is reinforced by the fresh default desktop background, a re-drawn, more saturated version of Leopard's default desktop. (Note that these are two entirely different images and not an attempt to demonstrate the effects of different gamma correction settings.)

    LeopardLeopard Snow LeopardSnow Leopard Dock Exposé spotlight effectDock Exposé spotlight effect

    But even beyond color correction, uniform to form, Apple could not resist adding a few graphical tweaks to the Snow Leopard interface. The most evident changes are related to the Dock. First, there's the fresh "spotlight" glance triggered by a click-and-hold on an application icon in the Dock. (This activates Exposé, but only for the windows belonging to the application that was clicked. More later.)

    Furthermore, any and every pop-up menus on the Dock—and only on the Dock—have a unique glance in Snow Leopard, complete with a custom selection appearance (which, for a change, does a passable job of matching the system-wide selection appearance setting).

    New Dock menu appearance. Mmmm… arbitrary.New Dock menu appearance. Mmmm… arbitrary.

    For Mac users of a inevitable age, these menus may bring to irony Apple's Hi-Tech appearance theme from the bad-old days of Copland. They're actually considerably more subtle, however. Note the translucent edges which accentuate the rounded corners. The gradient on the selection highlight is besides admirably restrained.

    Nevertheless, this is an entirely fresh glance for a solitary (albeit commonly used) application, and it does clash a bit with the default "slanty, shiny shelf" appearance of the Dock. But I've already had my squawk about that, and more. If the oath of Snow Leopard's appearance was to "first, carry out no harm," then I deem I'm inclined to give it a passing grade—almost.

    If I had to characterize what's wrong with Snow Leopard's visual additions with just two words, it'd be these: everything fades. Apple has sprinkled Core Animation fairy dust over seemingly every application in Snow Leopard. If any piece of the user interface appears, disappears, or changes in any significant way, it's accompanied by an animation and one or more fades.

    In moderation, such effects are fine. But in several instances, Snow Leopard crosses the line. Or rather, it crosses my line, which, it should be noted, is located far inside the territories of Candy Land. Others with a much lower tolerance for animations who are already galled by the frippery in Leopard and earlier releases will find limited to adore in Snow Leopard's visual changes.

    The one that really drove me over the edge is the fussy limited dance of the filename region that occurs in the Finder (surprise!) when renaming a file on the desktop. There's just something about so many cross-fades, color changes, and text offsets occurring so rapidly and concentrated into such a small region that makes me want to scream. And whether or not I'm actually waiting for these animations to finish before I can continue to employ my computer, it certainly feels that pass sometimes.

    Still, I must unenthusiastically prognosticate that most customary people (i.e., the ones who will not read this entire article) will either find these added visual touches delightful, or (much more likely) not notice them at all.


    Animation aside, the visual sameness of Snow Leopard presents a bit of a marketing challenge for Apple. Even beyond the obvious problem of how to promote an operating system upgrade with "no fresh features" to consumers, there's the issue of how to accumulate people to notice that this fresh product exists at all.

    In the run-up to Snow Leopard's release, Apple stuck to a modified version of Leopard's outer space theme. It was in the keynote slideshows, on the WWDC banners, on the developer release DVDs, and every over the Mac OS X section of Apple's website. The header image from Apple's Mac OS X webpage as of a week before Snow Leopard's release appears below. It's pretty gash and dried: outer space, stars, loaded purple nebula, lens flare.

    Snow. The final frontier.Snow. The final frontier.

    Then came the golden master of Snow Leopard, which, in a pleasant change from past releases, was distributed to developers a few weeks before Snow Leopard hit the shelves. Its installer introduced an entirely different glance which, as it turns out, was carried over to the retail packaging. For a change, let's line up the discs instead of the packaging (which is rapidly shrinking to barely wall the disc anyway). Here's Mac OS X 10.0 through 10.6, top to bottom and left to right. (The 10.0 and 10.1 discs looked essentially identical and relish been coalesced.)

    One of these things is not   fondness the others…One of these things is not fondness the others…

    Yep, it's a snow leopard. With actual snow on it. It's a bit on the nose for my taste, but it's not without its charms. And it does relish one expansive thing going for it: it's immediately recognizable as something fresh and different. "Unmistakable" is how I'd sum up the packaging. Eight years of the giant, centered, variously adorned "X" and then boom: a cat. There's limited desultory that anyone who's seen Leopard sitting on the shelf of their local Apple store for the past two years will fail to notice that this is a fresh product.

    (If you'd fondness your own picture of Snowy the snow leopard (that's right, I've named him), Apple was kindly enough to include a desktop background image with the OS. Self-loathing Windows users may download it directly.)

    Warning: internals ahead

    We've arrived at the start of the customary "internals" section. Snow Leopard is every about internal changes, and this is reflected in the content of this review. If you're only interested in the user-visible changes, you can skip ahead, but you'll be missing out on the meat of this review and the heart of Apple's fresh OS.

    64-bit: the road leads ever on

    Mac OS X started its journey to 64-bit back in 2003 with the release of Panther, which included the bare minimum uphold for the then-new PowerPC G5 64-bit CPU. In 2005, Tiger brought with it the ability to create uniform 64-bit processes—as long as they didn't link with any of the GUI libraries. Finally, Leopard in 2007 included uphold for 64-bit GUI applications. But again, there was a caveat: 64-bit uphold extended to Cocoa applications only. It was, effectively, the finish of the road for Carbon.

    Despite Leopard's seemingly impressive 64-bit bona fides, there are a few more steps before Mac OS X can achieve complete 64-bit nirvana. The diagrams below illustrate.

    64-bit in Mac OS X 10.4 Tiger 64-bit in Mac OS X 10.5 Leopard 64-bit in Mac OS X 10.6 Snow Leopard Mac OS X 10.4 Tiger Mac OS X 10.5 Leopard Mac OS X 10.6 Snow Leopard

    As we'll see, every that yellow in the Snow Leopard diagram represents its capability, not necessarily its default mode of operation.


    Snow Leopard is the first version of Mac OS X to ship with a 64-bit kernel ("K64" in Apple's parlance), but it's not enabled by default on most systems. The reason for this this is simple. Recall that there's no "mixed mode" in Mac OS X. At runtime, a process is either 32-bit or 64-bit, and can only load other code—libraries, plug-ins, etc.—of the same kind.

    An well-known class of plug-ins loaded by the kernel is device drivers. Were Snow Leopard to default to the 64-bit kernel, only 64-bit device drivers would load. And seeing as Snow Leopard is the first version of Mac OS X to include a 64-bit kernel, there'd be precious few of those on customers' systems on launch day.

    And so, by default, Snow Leopard boots with a 64-bit kernel only on Xserves from 2008 or later. I guess the assumption is that every of the devices commonly attached to an Xserve will be supported by 64-bit drivers supplied by Apple in Snow Leopard itself.

    Perhaps surprisingly, not every Macs with 64-bit processors are even able to boot into the 64-bit kernel. Though this may change in subsequent point releases of Snow Leopard, the table below lists every the Macs that are either capable of or default to booting K64. (To find the "Model name" of your Mac, select "About This Mac" from the Apple menu, then click the "More info…" button and read the "Model Identifier" line in the window that appears.)

    Product Model name K64 status Early 2008 Mac Pro MacPro3,1 Capable Early 2008 Xserve Xserve2,1 Default MacBook Pro 15"/17" MacBookPro4,1 Capable iMac iMac8,1 Capable UniBody MacBook Pro 15" MacBookPro5,1 Capable UniBody MacBook Pro 17" MacBookPro5,2 Capable Mac Pro MacPro4,1 Capable iMac iMac9,1 Capable Early 2009 Xserve Xserve3,1 Default

    For every K64-capable Macs, boot while holding down "6" and "4" keys simultaneously to select the 64-bit kernel. For a more permanent solution, employ the nvram command to add arch=x86_64 to your boot-args string, or edit the file /Library/Preferences/SystemConfiguration/ and add arch=x86_64 to the Kernel Flags string:

    ... <key>Kernel</key> <string>mach_kernel</string> <key>Kernel Flags</key> <string>arch=x86_64</string> ...

    To switch back to the 32-bit kernel, hold down the "3" and "2" keys during boot, or employ one of the techniques above, replacing "x86_64" with "i386".

    We've already discussed why, at least initially, you probably won't want to boot into K64. But as Snow Leopard adoption ramps up and 64-bit updates of existing kernel extensions become available, why might you actually want to employ the 64-bit kernel?

    The first reason has to carry out with RAM, and not in the pass you might think. Though Leopard uses a 32-bit kernel, Macs running Leopard can accommodate and employ far more RAM than the 4 GB circumscribe the "32-bit" qualifier might appear to imply. But as RAM sizes increase, there's another concern: address space depletion—not for applications, but for the kernel itself.

    As a 32-bit process, the kernel itself is limited to a 32-bit (i.e., 4GB) address space. That may not appear fondness a problem; after all, should the kernel really need more than 4GB of remembrance to carry out its job? But remember that piece of the kernel's job is to track and manage system memory. The kernel uses a 64-byte structure to track the status of each 4KB page of RAM used on the system.

    That's 64 bytes, not kilobytes. It hardly seems fondness a lot. But now regard a Mac in the not-too-distant future containing 96GB of RAM. (If this sounds ridiculous to you, deem of how ridiculous the 8GB of RAM in the Mac I'm typing on perquisite now would relish sounded to you five years ago.) Tracking 96GB of RAM requires 1.5GB of kernel address space. Using more than a third of the kernel's address space just to track remembrance is a pretty uncomfortable situation.

    A 64-bit kernel, on the other hand, has a virtually unlimited kernel address space (16 exabytes). K64 is an inevitable necessity, given the rapidly increasing size of system memory. Though you may not need it today on the desktop, it's already common for servers to relish double-digit gigabytes of RAM installed.

    The other thing K64 has going for it is speed. The x86 instruction set architecture has had a bit of a tortured history. When designing the x86-64 64-bit extension of the x86 architecture, AMD took the break to leave behind some of the ugliness of the past and include more modern features: more registers, fresh addressing modes, non-stack-based floating point capabilities, etc. K64 reaps these benefits. Apple makes the following claims about its performance:

  • 250% faster system summon entry point
  • 70% faster user/kernel remembrance copy
  • Focused benchmarking would endure these out, I'm sure. But in daily use, you're unlikely to be able to attribute any particular performance boost to the kernel. deem of K64 as removing bottlenecks from the few (usually server-based) applications that actually carry out exercise these aspects of the kernel heavily.

    If it makes you feel better to know that your kernel is operating more efficiently, and that, were you to actually relish 96GB of RAM installed, you would not risk starving the kernel of address space, and if you don't relish any 32-bit drivers that you absolutely need to use, then by every means, boot into the 64-bit kernel.

    For everyone else, my recommendation is to be cheerful that K64 will be ready and waiting for you when you eventually carry out need it—and gladden carry out hearten every the vendors that do kernel extensions that you faith about to add K64 uphold as soon as possible.

    Finally, this is worth repeating: gladden maintain in irony that you carry out not need to rush the 64-bit kernel in order to rush 64-bit applications or install more than 4GB of RAM in your Mac. Applications rush just fine in 64-bit mode on top of the 32-bit kernel, and even in earlier versions of Mac OS X it's been feasible to install and rob edge of much more than 4GB of RAM.

    64-bit applications

    While Leopard may relish brought with it uphold for 64-bit GUI applications, it actually included very few of them. In fact, by my count, only two 64-bit GUI applications shipped with Leopard: Xcode (an optional install) and Chess. And though Leopard made it feasible for third-party developers to relent 64-bit (albeit Leopard-only) GUI applications, very few have—sometimes due to ill-started realities, but most often because there's been no noble reason to carry out so, abandoning users of Mac OS X 10.4 or earlier in the process.

    Apple is now pushing the 64-bit transition much harder. This starts with leading by example. Snow Leopard ships with four end-user GUI applications that are not 64-bit: iTunes, Grapher, Front Row, and DVD Player. Everything else is 64-bit. The Finder, the Dock, Mail, TextEdit, Safari, iChat, Address Book, Dashboard, assist Viewer, Installer, Terminal, Calculator—you cognomen it, it's 64-bit.

    The second expansive carrot (or stick, depending on how you glance at it) is the continued lack of 32-bit uphold for fresh APIs and technologies. Leopard started the trend, leaving deprecated APIs behind and only porting the fresh ones to 64-bit. The improved Objective-C 2.0 runtime introduced in Leopard was besides 64-bit-only.

    Snow Leopard continues along similar lines. The Objective-C 2.1 runtime's non-fragile instance variables, exception model unified with C++, and faster vtable dispatch remain available only to 64-bit applications. But the most significant fresh 64-bit-only API is QuickTime X—significant enough to be addressed separately, so sojourn tuned.

    64-bits or bust

    All of this is Apple's not-so-subtle pass of telling developers that the time to paddle to 64-bit is now, and that 64-bit should be the default for every fresh applications, whether a developer thinks it's "needed" or not. In most cases, these fresh APIs relish no intrinsic connection to 64-bit. Apple has simply chosen to employ them as additional forms of persuasion.

    Despite every of the above, I'd still summon Snow Leopard merely the penultimate step in Mac OS X's journey to be 64-bit from top to bottom. I fully expect Mac OS X 10.7 to boot into the 64-bit kernel by default, to ship with 64-bit versions of every applications, plug-ins, and kernel extensions, and to leave even more legacy and deprecated APIs to fade away in the land of 32-bit.

    QuickTime X

    Apple did something a bit odd in Leopard when it neglected to port the C-based QuickTime API to 64-bit. At the time, it didn't appear fondness such a expansive deal. Mac OS X's transition to 64-bit had already spanned many years and several major versions. One could imagine that it just wasn't yet QuickTime's spin to paddle 64-bit.

    As it turns out, my terse but pessimistic assessment of the situation at the time was accurate: QuickTime got the "Carbon treatment". fondness Carbon, the venerable QuickTime API that they know and adore will not be making the transition to 64-bit—ever.

    To be clear, QuickTime the technology and QuickTime the brand will most definitely be coming to 64-bit. What's being left behind in 32-bit-only contour is the C-based API introduced in 1991 and built upon for 18 years thereafter. Its replacement in the world of 64-bit in Snow Leopard is the aptly named QuickTime X.

    The "X" in QuickTime X, fondness the one in in Mac OS X, is pronounced "ten." This is but the first of many eerie parallels. fondness Mac OS X before it, QuickTime X:

  • aims to do a immaculate fracture from its predecessor
  • is based on technology originally developed for another platform
  • includes transparent compatibility with its earlier incarnation
  • promises better performance and a more modern architecture
  • lacks many well-known features in its initial release
  • Maximum available Mac CPU  hasten (MHz)Maximum available Mac CPU hasten (MHz)

    Let's rob these one at a time. First, why is a immaculate fracture needed? save simply, QuickTime is old—really old. The horribly blocky, postage-stamp-size video displayed by its initial release in 1991 was considered a technological tour de force.

    At the time, the fastest Macintosh money could buy contained a 25 MHz CPU. The ridiculous chart to the perquisite is meant to hammer home this point. Forward-thinking design can only accumulate you so far. The shape of the world a technology is born into eventually, inevitably dictates its fate. This is especially uniform for long-lived APIs fondness QuickTime with a sturdy bent towards backward compatibility.

    As the first successful implementation of video on a personal computer, it's frankly astounding that the QuickTime API has lasted as long as it has. But the world has moved on. Just as Mac OS organize itself mired in a ghetto of cooperative multitasking and unprotected memory, QuickTime limps into 2009 with antiquated notions of concurrency and subsystem layering baked into its design.

    When it came time to write the video-handling code for the iPhone, the latest version of QuickTime, QuickTime 7, simply wasn't up to the task. It had grown too bloated and inefficient during its life on the desktop, and it lacked noble uphold for the GPU-accelerated video playback necessary to exploit modern video codecs on a handheld (even with a CPU sixteen times the clock hasten of any available in a Mac when QuickTime 1.0 was released). And so, Apple created a tight, modern, GPU-friendly video playback engine that could fit comfortably within the RAM and CPU constraints of the iPhone.

    Hmm. An aging desktop video API in need of a replacement. A fresh, fresh video library with noble performance even on (comparatively) anemic hardware. Apple connected the dots. But the trick is always in the transition. Happily, this is Apple's forte. QuickTime itself has already lived on three different CPU architectures and three entirely different operating systems.

    The switch to 64-bit is yet another (albeit less dramatic) inflection point, and Apple has chosen it to imprint the border between the mature QuickTime 7 and the fresh QuickTime X. It's done this in Snow Leopard by limiting every employ of QuickTime by 64-bit applications to the QTKit Objective-C framework.

    QTKit's fresh world order

    QTKit is not new; it began its life in 2005 as a more native-feeling interface to QuickTime 7 for Cocoa applications. This extra layer of abstraction is the key to the QuickTime X transition. QTKit now hides within its object-oriented walls both QuickTime 7 and QuickTime X. Applications employ QTKit as before, and behind the scenes QTKit will pick whether to employ QuickTime 7 or QuickTime X to fulfill each request.

    If QuickTime X is so much better, why doesn't QTKit employ it for everything? The acknowledge is that QuickTime X, fondness its Mac OS X namesake, has very limited capabilities in its initial release. While QuickTime X supports playback, capture, and exporting, it does not uphold general-purpose video editing. It besides supports only "modern" video formats—basically, anything that can be played by an iPod, iPhone, or Apple TV. As for other video codecs, well, you can forget about handling them with plug-ins because QuickTime X doesn't uphold those either.

    For every one of the cases where QuickTime X is not up to the job, QuickTime 7 will fill in. Cutting, copying, and pasting portions of a video? QuickTime 7. Extracting individual tracks from a movie? QuickTime 7. Playing any movie not natively supported by an existing Apple handheld device? QuickTime 7. Augmenting QuickTime's codec uphold using a plug-in of any kind? You guessed it: QuickTime 7.

    But wait a second. If QTKit is the only pass for a 64-bit application to employ QuickTime, and QTKit multiplexes between QuickTime 7 and QuickTime X behind the scenes, and QuickTime 7 is 32-bit-only, and Mac OS X does not uphold "mixed mode" processes that can execute both 32-bit and 64-bit code, then how the heck does a 64-bit process carry out anything that requires the QuickTime 7 back-end?

    To find out, fire up the fresh 64-bit QuickTime Player application (which will be addressed separately later) and open a movie that requires QuickTime 7. Let's say, one that uses the Sorenson video codec. (Remember that? noble times.) positive enough, it plays just fine. But search for "QuickTime" in the Activity Monitor application and you'll descry this:

    Pretty sneaky, sis: 32-bit QTKitServer processPretty sneaky, sis: 32-bit QTKitServer process

    And the acknowledge is revealed. When a 64-bit application using QTKit requires the services of the 32-bit-only QuickTime 7 back-end, QTKit spawns a separate 32-bit QTKitServer process to carry out the travail and communicate the results back to the originating 64-bit process. If you leave Activity Monitor open while using the fresh QuickTime Player application, you can watch the QTKitServer processes approach and paddle as needed. This is every handled transparently by the QTKit framework; the application itself need not be conscious of these machinations.

    Yes, it's going to be a long, long time before QuickTime 7 disappears completely from Mac OS X (at least Apple was kindly enough not to summon it "QuickTime Classic"), but the path forward is clear. With each fresh release of Mac OS X, expect the capabilities of QuickTime X to expand, and the number of things that still require QuickTime 7 to decrease. In Mac OS X 10.7, for example, I imagine that QuickTime X will gain uphold for plug-ins. And surely by Mac OS X 10.8, QuickTime X will relish complete video editing support. every this will be happening beneath the unifying facade of QTKit until, eventually, the QuickTime 7 back-end is no longer needed at all.

    Say what you mean

    In the meantime, perhaps surprisingly, many of the current limitations of QuickTime X actually highlight its unique advantages and inform the evolving QTKit API. Though there is no direct pass for a developer to request that QTKit employ the QuickTime X back-end, there are several circuitous means to influence the decision. The key is the QTKit API, which relies heavily on the concept of intent.

    QuickTime versions 1 through 7 employ a solitary representation of every media resources internally: a Movie object. This representation includes information about the individual tracks that do up the movie, the sample tables for each track, and so on—all the information QuickTime needs to understand and exploit the media.

    This sounds worthy until you realize that to carry out anything with a media resource in QuickTime requires the construction of this comprehensive Movie object. regard playing an MP3 file with QuickTime, for example. QuickTime must create its internal Movie expostulate representation of the MP3 file before it can initiate playback. Unfortunately, the MP3 container format seldom contains comprehensive information about the structure of the audio. It's usually just a stream of packets. QuickTime must laboriously scan and parse the entire audio stream in order to complete the Movie object.

    QuickTime 7 and earlier versions do this process less painful by doing the scanning and parsing incrementally in the background. You can descry this in many QuickTime-based player applications in the contour of a progress bar overlaid on the movie controller. The image below shows a 63MB MP3 podcast loading in the Leopard version of QuickTime Player. The shaded portion of the movie timeline slowly fills the dotted region from left to right.

    QuickTime 7 doing more  travail than necessary

    QuickTime 7 doing more travail than necessary

    Though playback can initiate almost immediately (provided you play from the beginning, that is) it's worthwhile to rob a step back and regard what's going on here. QuickTime is creating a Movie expostulate suitable for any operation that QuickTime can perform: editing, track extraction or addition, exporting, you cognomen it. But what if every I want to carry out is play the file?

    The inconvenience is, the QuickTime 7 API lacks a pass to express this kindly of intent. There is no pass to squawk to QuickTime 7, "Just open this file as quickly as feasible so that I can play it. Don't bother reading every solitary byte of the file from the disk and parsing it to determine its structure just in case I resolve to edit or export the content. That is not my intent. Please, just open it for playback."

    The QTKit API in Snow Leopard provides exactly this capability. In fact, the only pass to be eligible for the QuickTime X back-end at every is to explicitly express your intent not to carry out anything QuickTime X cannot handle. Furthermore, any attempt to fulfill an operation that lies outside your previously expressed intent will reason QTKit to raise an exception.

    The intent mechanism is besides the pass that the fresh features of QuickTime X are exposed, such as the ability to asynchronously load great or distantly located (e.g., over a slow network link) movie files without blocking the UI running on the main thread of the application.

    Indeed, there are many reasons to carry out what it takes to accumulate on board the QuickTime X train. For the media formats it supports, QuickTime X is less taxing on the CPU during playback than QuickTime 7. (This is beyond the fact that QuickTime X does not dissipate time preparing its internal representation of the movie for editing and export when playback is every that's desired.) QuickTime X besides supports GPU-accelerated playback of H.264, but, in this initial release, only on Macs equipped with an NVIDIA 9400M GPU (i.e., some 2009 iMacs and several models of MacBooks from 2008 and 2009). Finally, QuickTime X includes comprehensive ColorSync uphold for video, which is long overdue.

    The X factor

    This is just the start of a long journey for QuickTime X, and seemingly not a very auspicious one, at that. A QuickTime engine with no editing support? No plug-ins? It seems ridiculous to release it at all. But this has been Apple's pass in recent years: steady, deliberate progress. Apple aims to ship no features before their time.

    As anxious as developers may be for a full-featured, 64-bit successor to the QuickTime 7 engine, Apple itself is sitting on top of one of the largest QuickTime-riddled (and Carbon-addled, to boot) code bases in the industry: Final gash Studio. Thus far, It remains stuck in 32-bit. To squawk that Apple is "highly motivated" to extend the capabilities of QuickTime X would be an understatement.

    Nevertheless, don't expect Apple to rush forward foolishly. Duplicating the functionality of a continually developed, 18-year-old API will not occur overnight. It will rob years, and it will be even longer before every well-known Mac OS X application is updated to employ QTKit exclusively. Transitions. Gotta adore 'em.

    File system API unification

    Mac OS X has historically supported many different ways of referring to files on disk from within an application. Plain-old paths (e.g., /Users/john/Documents/myfile) are supported at the lowest levels of the operating system. They're simple, predictable, but perhaps not such a worthy idea to employ as the only pass an application tracks files. regard what happens if an application opens a file based on a path string, then the user moves that file somewhere else while it's still being edited. When the application is instructed to save the file, if it only has the file path to travail with, it will finish up creating a fresh file in the mature location, which is almost certainly not what the user wanted.

    Classic Mac OS had a more sophisticated internal representation of files that enabled it to track files independent of their actual locations on disk. This was done with the assist of the unique file ids supported by HFS/HFS+. The Mac OS X incarnation of this concept is the FSRef data type.

    Finally, in the modern age, URLs relish become the de facto representation for files that may be located somewhere other than the local machine. URLs can besides refer to local files, but in that case they relish every the same disadvantages as file paths.

    This diversity of data types is reflected in Mac OS X's file system APIs. Some functions rob file path as arguments, some expect opaque references to files, and still others travail only with URLs. Programs that employ these APIs often expend a lot of their time converting file references from one representation to another.

    The situation is similar when it comes to getting information about files. There are a huge number of file system metadata retrieval functions at every levels of the operating system, and no solitary one of them is comprehensive. To accumulate every available information about a file on disk requires making several separate calls, each of which may expect a different type of file reference as an argument.

    Here's an sample Apple provided at WWDC. Opening a solitary file in the Leopard version of the Preview image viewer application results in:

  • Four conversions of an FSRef to a file path
  • Ten conversions of a file path to an FSRef
  • Twenty-five calls to getattrlist()
  • Eight calls to stat()/lstat()
  • Four calls to open()/close()
  • In Snow Leopard, Apple has created a new, unified, comprehensive set of file system APIs built around a solitary data type: URLs. But these are URL "objects"—namely, the opaque data types NSURL and CFURL, with a toll-free bridge between them—that relish been imbued with every the desirable attributes of an FSRef.

    Apple settled on these data types because their opaque nature allowed this kindly of enhancement, and because there are so many existing APIs that employ them. URLs are besides the most future-proof of every the choices, with the scheme portion providing nearly unlimited flexibility for fresh data types and access mechanisms. The fresh file system APIs built around these opaque URL types uphold caching and metadata prefetching for a further performance boost.

    There's besides a fresh on-disk representation called a Bookmark (not to be confused with a browser bookmark) which is fondness a more network-savvy replacement for classic Mac OS aliases. Bookmarks are the most robust pass to create a reference to a file from within another file. It's besides feasible to attach whimsical metadata to each Bookmark. For example, if an application wants to maintain a persistent list of "favorite" files plus some application-specific information about them, and it wants to be resilient to any movement of these files behind its back, Bookmarks are the best tool for the job.

    I mention every of this not because I expect file system APIs to be every that inquisitive to people without my particular fascination with this piece of the operating system, but because, fondness Core Text before it, it's an indication of exactly how youthful Mac OS X really is as a platform. Even after seven major releases, Mac OS X is still struggling to paddle out from the shadow of its three ancestors: NeXTSTEP, classic Mac OS, and BSD Unix. Or perhaps it just goes to exhibit how ruthlessly Apple's core OS team is driven to supplant mature and crusty APIs and data types with new, more modern versions.

    It will be a long time before the benefits of these changes trickle down (or is it up?) to end-users in the contour of Mac applications that are written or modified to employ these fresh APIs. Most well-written Mac applications already exhibit most of the desirable behavior. For example, the TextEdit application in Leopard will correctly detect when a file it's working on has moved.

    TextEdit: a  noble Mac OS X citizenTextEdit: a noble Mac OS X citizen

    Of course, the key modifier here is "well-written." Simplifying the file system APIs means that more developers will be willing to expend the effort—now greatly reduced—to provide such user-friendly behaviors. The accompanying performance boost is just icing on the cake, and one more reason that developers might pick to alter their existing, working application to employ these fresh APIs.

    Doing more with more

    Moore's Law is widely cited in technology circles—and besides widely misunderstood. It's most often used as shorthand for "computers double in hasten every year or so," but that's not what Gordon Moore wrote at all. His 1965 article in Electronics magazine touched on many topics in the semiconductor industry, but if it had to be summed up in a solitary "law", it would be, roughly, that the number of transistors that fit onto a square inch of silicon doubles every 12 months.

    Moore later revised that to two years, but the time epoch is not what people accumulate wrong. The problem is confusing a doubling of transistor density with a doubling of "computer speed." (Even more problematic is declaring a "law" based on a solitary paper from 1965, but we'll save that aside for now. For a more thorough discussion of Moore's Law, gladden read this classic article by Jon Stokes.)

    For decades, each augment in transistor density was, in fact, accompanied by a comparable augment in computing hasten thanks to ever-rising clock speeds and the dawn of superscalar execution. This worked great—existing code ran faster on each fresh CPU—until the grim realities of power density save an finish to the fun.

    Moore's Law continues, at least for now, but their ability to do code rush faster with each fresh augment in transistor density has slowed considerably. The free lunch is over. CPU clock speeds relish stagnated for years, many times actually going backwards. (The latest top-of-the-line 2009 Mac Pro contains a 2.93 GHz CPU, whereas the 2008 model could be equipped with a 3.2 GHz CPU.) Adding execution units to a CPU has besides long since reached the point of diminishing returns, given the limits of instruction-level parallelism in common application code.

    And yet we've still got every these fresh transistors raining down on us, more every year. The challenge is to find fresh ways to employ them to actually do computers faster.

    Thus far, the semiconductor industry's acknowledge has been to give us more of what they already have. Where once a CPU contained a solitary rational processing unit, now CPUs in even the lowliest desktop computers accommodate two processor cores, with high-end models sporting two chips with eight rational cores each. Granted, the cores themselves are besides getting faster, usually by doing more at the same clock hasten as their predecessors, but that's not happening at nearly the rate that the cores are multiplying.

    Unfortunately, generally speaking, a dual-core CPU will not rush your application twice as swift as a single-core CPU. In fact, your application probably won't rush any faster at every unless it was written to rob edge of more than just a solitary rational CPU. Presented with a glut of transistors, chipmakers relish turned around and provided more computing resources than programmers know what to carry out with, transferring much of the responsibility for making computers faster to the software guys.

    We're with the operating system and we're here to help

    It's into this environment that Snow Leopard is born. If there's one responsibility (aside from security) that an operating system vendor should feel in the year 2009, it's finding a pass for applications—and the OS itself—to utilize the ever-growing wealth of computing resources at their disposal. If I had to pick solitary technological "theme" for Snow Leopard, this would be it: helping developers utilize every this newfound silicon; helping them carry out more with more.

    To that end, Snow Leopard includes two significant fresh APIs backed by several smaller, but equally well-known infrastructure improvements. We'll start at the bottom with, believe it or not, the compiler.

    LLVM and Clang

    Apple made a strategic investment in the LLVM open source project several years ago. I covered the fundamentals of LLVM in my Leopard review. (If you're not up to speed, gladden trap up on the topic before continuing.) In it, I described how Leopard used LLVM to provide dramatically more efficient JIT-compiled software implementations of OpenGL functions. I ended with the following admonition:

    Don't be misled by its humble employ in Leopard; Apple has magnificient plans for LLVM. How grand? How about swapping out the guts of the gcc compiler Mac OS X uses now and replacing them with the LLVM equivalents? That project is well underway. Not ambitious enough? How about ditching gcc entirely, replacing it with a completely fresh LLVM-based (but gcc-compatible) compiler system? That project is called Clang, and it's already yielded some impressive performance results.

    With the introduction of Snow Leopard, it's official: Clang and LLVM are the Apple compiler strategy going forward. LLVM even has a snazzy fresh logo, a not-so-subtle homage to a well-known compiler design textbook:

    LLVM! Clang! Rawr!

    LLVM! Clang! Rawr!

    Apple now offers a total of four compilers for Mac OS X: GCC 4.0, GCC 4.2, LLVM-GCC 4.2 (the GCC 4.2 front-end combined with an LLVM back-end), and Clang, in order of increasing LLVM-ness. Here's a diagram:

    Mac OS X compilers

    Mac OS X compilers

    All of these compilers are binary-compatible on Mac OS X, which means you can, for example, build a library with one compiler and link it into an executable built with another. They're besides every command-line and source-compatible—in theory, anyway. Clang does not yet uphold some of the more esoteric features of GCC. Clang besides only supports C, Objective-C, and a limited bit of C++ (Clang(uage), accumulate it?) whereas GCC supports many more. Apple is committed to replete C++ uphold for Clang, and hopes to travail out the remaining GCC incompatibilities during Snow Leopard's lifetime.

    Clang brings with it the two headline attributes you expect in a hot, fresh compiler: shorter compile times and faster executables. In Apple's testing with its own applications such as iCal, Address Book, and Xcode itself, plus third-party applications fondness Adium and Growl, Clang compiles nearly three times faster than GCC 4.2. As for the hasten of the finished product, the LLVM back-end, whether used in Clang or in LLVM-GCC, produces executables that are 5-25% faster than those generated by GCC 4.2.

    Clang is besides more developer-friendly than its GCC predecessors. I concede that this topic doesn't relish much to carry out with taking edge of multiple CPU cores and so on, but it's positive to be the first thing that a developer actually notices when using Clang. Indulge me.

    For starters, Clang is embeddable, so Xcode can employ the same compiler infrastructure for interactive features within the IDE (symbol look-up, code completion, etc.) as it uses to compile the final executable. Clang besides creates and preserves more extensive metadata while compiling, resulting in much better error reporting. For example, when GCC tells you this:

    GCC error message for an unknown type

    It's not exactly transparent what the problem is, especially if you're fresh to C programming. Yes, every you hotshots already know what the problem is (especially if you saw this sample at WWDC), but I deem everyone can disagree that this error, generated by Clang, is a lot more helpful:

    Clang error message for an unknown type

    Maybe a novice still wouldn't know what to do, but at least it's transparent where the problem lies. Figuring out why the compiler doesn't know about NSString is a much more focused chore than can be derived from GCC's cryptic error.

    Even when the message is clear, the context may not be. rob this error from GCC:

    GCC error message for  harmful operands

    Sure, but there are four "+" operators on that solitary line. Which one has the problematic operands? Thanks to its more extensive metadata, Clang can pinpoint the problem:

    Clang error message for  harmful operands

    Sometimes the error is perfectly clear, but it just seems a bit off, fondness this situation where jumping to the error as reported by GCC puts you on the line below where you actually want to add the missing semicolon:

    GCC error message for missing semicolon

    The limited things count, you know? Clang goes that extra mile:

    Clang error message for missing semicolon

    Believe it or not, stuff fondness this means a lot to developers. And then there are the not-so-little things that connote even more, fondness the LLVM-powered static analyzer. The image below shows how the static analyzer displays its discovery of a feasible bug.

    OH HAI I  organize UR BUGOH HAI I organize UR BUG

    Aside from the whimsy of the limited arrows (which, admit it, are adorable), the actual bug it's highlighting is something that every programmer can imagine creating (say, through some hasty editing). The static analyzer has determined that there's at least one path through this set of nested conditionals that leaves the myName variable uninitialized, thus making the attempt to dispatch the mutableCopy message in the final line potentially dangerous.

    I'm positive Apple is going hog-wild running the static analyzer on every of its applications and the operating system itself. The prospect of an automated pass to ascertain bugs that may relish existed for years in the depths of a huge codebase is almost pornographic to developers—platform owners in particular. To the degree that Mac OS X 10.6.0 is more bug-free than the previous 10.x.0 releases, LLVM surely deserves some significant piece of the credit.

    Master of the house

    By committing to a Clang/LLVM-powered future, Apple has finally taken complete control of its development platform. The CodeWarrior experience apparently convinced Apple that it's unwise to faith on a third party for its platform's development tools. Though it's taken many years, I deem even the most diehard Metrowerks fan would relish to disagree that Xcode in Snow Leopard is now a pretty damn noble IDE.

    After years of struggling with the disconnect between the goals of the GCC project and its own compiler needs, Apple has finally gash the apron strings. OK, granted, GCC 4.2 is still the default compiler in Snow Leopard, but this is a transitional phase. Clang is the recommended compiler, and the focus of every of Apple's future efforts.

    I know what you're thinking. This is swell and all, but how are these compilers helping developers better leverage the expanding swarm of transistors at their disposal? As you'll descry in the following sections, LLVM's scaly, metallic head pops up in a few key places.


    In Snow Leopard, Apple has introduced a C language extension called "blocks." Blocks add closures and anonymous functions to C and the C-derived languages C++, Objective-C, and Objective C++.

    These features relish been available in dynamic programming languages such as Lisp, Smalltalk, Perl, Python, Ruby, and even the unassuming JavaScript for a long time (decades, in the case of Lisp—a fact gladly offered by its practitioners). While dynamic-language programmers rob closures and anonymous functions for granted, those who travail with more traditional, statically compiled languages such as C and its derivatives may find them quite exotic. As for non-programmers, they likely relish no interest in this topic at all. But I'm going to attempt an explanation nonetheless, as blocks contour the foundation of some other inquisitive technologies to be discussed later.

    Perhaps the simplest pass to interpret blocks is that they do functions another contour of data. C-derived languages already relish duty pointers, which can be passed around fondness data, but these can only point to functions created at compile time. The only pass to influence the deportment of such a duty is by passing different arguments to the duty or by setting global variables which are then accessed from within the function. Both of these approaches relish expansive disadvantages

    Passing arguments becomes cumbersome as their number and complexity grows. Also, it may be that you relish limited control over the arguments that will be passed to your function, as is often the case with callbacks. To compensate, you may relish to bundle up every of your inquisitive status into a context expostulate of some kind. But when, how, and by whom that context data will be disposed of can be difficult to pin down. Often, a second callback is required for this. It's every quite a pain.

    As for the employ of global variables, in addition to being a well-known anti-pattern, it's besides not thread-safe. To do it so requires locks or some other contour of mutual exclusion to preclude multiple invocations of the same duty from stepping on each other's toes. And if there's anything worse than navigating a sea of callback-based APIs, it's manually dealing with thread safety issues.

    Blocks bypass every of these problems by allowing functional blobs of code—blocks—to be defined at runtime. It's easiest to understand with an example. I'm going to start by using JavaScript, which has a bit friendlier syntax, but the concepts are the same.

    b = get_number_from_user(); multiplier = function(a) { recrudesce a * b };

    Here I've created a duty named multiplier that takes a solitary argument, a, and multiplies it by a second value, b, that's provided by the user at runtime. If the user supplied the number 2, then a summon to multiplier(5) would recrudesce the value 10.

    b = get_number_from_user(); // assume it's 2 multiplier = function(a) { recrudesce a * b }; r = multiplier(5); // 5 * 2 = 10

    Here's the sample above done with blocks in C.

    b = get_number_from_user(); // assume it's 2 multiplier = ^ int (int a) { recrudesce a * b; }; r = multiplier(5); // 5 * 2 = 10

    By comparing the JavaScript code to the C version, I hope you can descry how it works. In the C example, that limited caret ^ is the key to the syntax for blocks. It's kindly of ugly, but it's very C-like in that it parallels the existing C syntax for duty pointers, with ^ in residence of *, as this sample illustrates:

    /* A duty that takes a solitary integer controversy and returns a pointer to a duty that takes two integer arguments and returns a floating-point number. */ float (*func2(int a))(int, int); /* A duty that takes a solitary integer controversy and returns a secrete that takes two integer arguments and returns a floating-point number. */ float (^func1(int a))(int, int);

    You'll just relish to faith me when I divulge you that this syntax actually makes sense to seasoned C programmers.

    Now then, does this connote that C is suddenly a dynamic, high-level language fondness JavaScript or Lisp? Hardly. The existing distinction between the stack and the heap, the rules governing automatic and static variables, and so on are every still in replete effect. Plus, now there's a entire fresh set of rules for how blocks interact with each of these things. There's even a fresh __block storage type attribute to further control the scope and lifetime of values used in blocks.

    All of that said, blocks are still a huge win in C. Thanks to blocks, the friendlier APIs long enjoyed by dynamic languages are now feasible in C-derived languages. For example, suppose you want to apply some operation to every line in a file. To carry out so in a low-level language fondness C requires some amount of boilerplate code to open and read from the file, exploit any errors, read each line into a buffer, and immaculate up at the end.

    FILE *fp = fopen(filename, "r"); if (fp == NULL) { perror("Unable to open file"); } else { char line[MAX_LINE]; while (fgets(line, MAX_LINE, fp)) { work; work; work; } fclose(fp); }

    The piece in bold is an abstract representation of what you're planning to carry out to each line of the file. The rest is the literal boilerplate code. If you find yourself having to apply varying operations to every line of many different files, this boilerplate code gets tedious.

    What you'd fondness to be able to carry out is factor it out into a duty that you can call. But then you're faced with the problem of how to express the operation you'd fondness to fulfill on each line of the file. In the middle of each secrete of boilerplate may be many lines of code expressing the operation to be applied. This code may reference or modify local variables which are affected by the runtime deportment of the program, so traditional duty pointers won't work. What to do?

    Thanks to blocks, you can define a duty that takes a filename and a secrete as arguments. This gets every the uninteresting code out of your face.

    foreach_line(filename, ^ (char *line) { work; work; work; });

    What's left is a much clearer expression of your intent, with less surrounding noise. The controversy after filename is a literal secrete that takes a line of text as an argument.

    Even when the volume of boilerplate is small, the simplicity and clarity premium is still worthwhile. regard the simplest feasible loop that executes a fixed number of times. In C-based languages, even that basic construct offers a surprising number of opportunities for bugs. Let's do_something() 10 times:

    for (int i = 0; i <= 10; i++) { do_something(); }

    Oops, I've got a limited bug there, don't I? It happens to the best of us. But why should this code be more complicated than the sentence describing it. carry out something 10 times! I never want to screw that up again. Blocks can help. If they just invest a limited effort up front to define a helper function:

    typedef void (^work_t)(void); void repeat(int n, work_t block) { for (int i = 0; i < n; ++i) block(); }

    We can deport the bug for good. Now, repeating any whimsical secrete of code a specific number of times is every but idiot-proof:

    repeat(10, ^{ do_something() }); repeat(20, ^{ do_other_thing() });

    And remember, the secrete controversy to repeat() can accommodate exactly the same kindly of code, literally copied and pasted, that would relish appeared within a traditional for loop.

    All these possibilities and more relish been well explored by dynamic languages: map, reduce, collect, etc. Welcome, C programmers, to a higher order.

    Apple has taken these lessons to heart, adding over 100 fresh APIs that employ blocks in Snow Leopard. Many of these APIs would not be feasible at every without blocks, and every of them are more elegant and concise than they would be otherwise.

    It's Apple purpose to submit blocks as an official extension to one or more of the C-based languages, though it's not yet transparent which standards bodies are receptive to the proposal. For now, blocks are supported by every four of Apple's compilers in Mac OS X.

    Concurrency in the actual world: a prelude

    The struggle to do efficient employ of a great number of independent computing devices is not new. For decades, the realm of high-performance computing has tackled this problem. The challenges faced by people writing software for supercomputers many years ago relish now trickled down to desktop and even mobile computing platforms.

    In the PC industry, some people saw this coming earlier than others. Almost 20 years ago, be Inc. was formed around the idea of creating a PC platform unconstrained by legacy limitations and entirely prepared for the coming abundance of independent computing units on the desktop. To that end, be created the BeBox, a dual-CPU desktop computer, and BeOS, a brand-new operating system.

    The signature trap phrase for BeOS was "pervasive multithreading." The BeBox and other machines running BeOS leveraged every ounce of the diminutive (by today's standards, anyway) computing resources at their disposal. The demos were impressive. A dual 66 MHz machine (don't do me exhibit another graph) could play multiple videos simultaneously while besides playing several audio tracks from a CD—some backwards— and every the while, the user interface remained completely responsive.

    Let me divulge you, having lived through this epoch myself, the experience was mind-blowing at the time. BeOS created instant converts out of hundreds of technology enthusiasts, many of whom maintain that today's desktop computing experience still doesn't match the responsiveness of BeOS. This is certainly uniform emotionally, if not necessarily literally.

    After nearly purchasing be in the late 1990s, Apple bought NeXT instead, and the rest is history. But had Apple gone with pass be instead, Mac developers might relish had a harsh road ahead. While every that pervasive multithreading made for impressive technology demos and a worthy user experience, it could be extremely demanding on the programmer. BeOS was every about threads, going so far as to maintain a separate thread for each window. Whether you liked it or not, your BeOS program was going to be multithreaded.

    Parallel programming is notoriously hard, with the manual management of POSIX-style threads representing the profound finish of that pool. The best programmers in the world are hard-pressed to create great multithreaded programs in low-level languages fondness C or C++ without finding themselves impaled on the spikes of deadlock, race conditions, and other perils inherent in the employ of in multiple simultaneous threads of execution that partake the same remembrance space. Extremely observant application of locking primitives is required to avoid performance-robbing levels of contention for shared data—and the bugs, oh the bugs! The term "Heisenbug" may as well relish been invented for multithreaded programming.

    Nineteen years after be tilted at the windmill of the widening swath of silicon in desktop PCs, the challenge has only grown. Those transistors are out there, man—more than ever before. Single-threaded programs on today's high-end desktop Macs, even when using "100%" CPU, extend but a solitary glowing tower in a sea of sixteen otherwise vacant lanes on a CPU monitor window.

    A wide-open  unpretentious of transistorsA wide-open unpretentious of transistors

    And woe be unto the user if that pegged CPU core is running the main thread of a GUI application on Mac OS X. A CPU-saturated main thread means no fresh user inputs are being pulled off the event queue by the application. A few seconds of that and an mature friend makes its appearance: the spinning beach ball of death.


    Nooooooooo!!! Image from The Iconfactory

    This is the enemy: hardware with more computing resources than programmers know what to carry out with, most of it completely idle, and every the while the user is utterly blocked in his attempts to employ the current application. What's Snow Leopard's answer? Read on…

    Grand Central Dispatch Apple's GCD branding: <a href="">Railfan</a> <a href="">service</a>Apple's GCD branding: Railfan service

    Snow Leopard's acknowledge to the concurrency conundrum is called magnificient Central Dispatch (GCD). As with QuickTime X, the cognomen is extremely apt, though this is not entirely transparent until you understand the technology.

    The first thing to know about GCD is that it's not a fresh Cocoa framework or similar special-purpose frill off to the side. It's a unpretentious C library baked into the lowest levels of Mac OS X. (It's in libSystem, which incorporates libc and the other code that sits at the very bottom of userspace.)

    There's no need to link in a fresh library to employ GCD in your program. Just #include <dispatch/dispatch.h> and you're off to the races. The fact that GCD is a C library means that it can be used from every of the C-derived languages supported on Mac OS X: Objective-C, C++, and Objective-C++.

    Queues and threads

    GCD is built on a few simple entities. Let's start with queues. A queue in GCD is just what it sounds like. Tasks are enqueued, and then dequeued in FIFO order. (That's "First In, First Out," just fondness the checkout line at the supermarket, for those who don't know and don't want to ensue the link.) Dequeuing the chore means handing it off to a thread where it will execute and carry out its actual work.

    Though GCD queues will hand tasks off to threads in FIFO order, several tasks from the same queue may be running in parallel at any given time. This animation demonstrates.

    A magnificient Central Dispatch queue in action

    You'll notice that chore B completed before chore A. Though dequeuing is FIFO, chore completion is not. besides note that even though there were three tasks enqueued, only two threads were used. This is an well-known feature of GCD which we'll contend shortly.

    But first, let's glance at the other kindly of queue. A serial queue works just fondness a customary queue, except that it only executes one chore at a time. That means chore completion in a serial queue is besides FIFO. Serial queues can be created explicitly, just fondness customary queues, but each application besides has an implicit "main queue" which is a serial queue that runs on the main thread.

    The animation above shows threads appearing as travail needs to be done, and disappearing as they're no longer needed. Where carry out these threads approach from and where carry out they paddle when they're done? GCD maintains a global pool of threads which it hands out to queues as they're needed. When a queue has no more pending tasks to rush on a thread, the thread goes back into the pool.

    This is an extremely well-known aspect of GCD's design. Perhaps surprisingly, one of the most difficult parts of extracting maximum performance using traditional, manually managed threads is figuring out exactly how many threads to create. Too few, and you risk leaving hardware idle. Too many, and you start to expend a significant amount of time simply shuffling threads in and out of the available processor cores.

    Let's squawk a program has a problem that can be split into eight separate, independent units of work. If this program then creates four threads on an eight-core machine, is this an sample of creating too many or too few threads? Trick question! The acknowledge is that it depends on what else is happening on the system.

    If six of the eight cores are totally saturated doing some other work, then creating four threads will just require the OS to dissipate time rotating those four threads through the two available cores. But wait, what if the process that was saturating those six cores finishes? Now there are eight available cores but only four threads, leaving half the cores idle.

    With the exception of programs that can reasonably expect to relish the entire machine to themselves when they run, there's no pass for a programmer to know ahead of time exactly how many threads he should create. Of the available cores on a particular machine, how many are in use? If more become available, how will my program know?

    The bottom line is that the optimal number of threads to save in flight at any given time is best determined by a single, globally conscious entity. In Snow Leopard, that entity is GCD. It will maintain zero threads in its pool if there are no queues that relish tasks to run. As tasks are dequeued, GCD will create and dole out threads in a pass that optimizes the employ of the available hardware. GCD knows how many cores the system has, and it knows how many threads are currently executing tasks. When a queue no longer needs a thread, it's returned to the pool where GCD can hand it out to another queue that has a chore ready to be dequeued.

    There are further optimizations inherent in this scheme. In Mac OS X, threads are relatively heavyweight. Each thread maintains its own set of register values, stack pointer, and program counter, plus kernel data structures tracking its security credentials, scheduling priority, set of pending signals and signal masks, etc. It every adds up to over 512 KB of overhead per thread. Create a thousand threads and you've just burned about a half a gigabyte of remembrance and kernel resources on overhead alone, before even considering the actual data within each thread.

    Compare a thread's 512 KB of baggage with GCD queues which relish a mere 256 bytes of overhead. Queues are very lightweight, and developers are encouraged to create as many of them as they need—thousands, even. In the earlier animation, when the queue was given two threads to process its three tasks, it executed two tasks on one of the threads. Not only are threads heavyweight in terms of remembrance overhead, they're besides relatively costly to create. Creating a fresh thread for each chore would be the worst feasible scenario. Every time GCD can employ a thread to execute more than one task, it's a win for overall system efficiency.

    Remember the problem of the programmer trying to figure out how many threads to create? Using GCD, he doesn't relish to worry about that at all. Instead, he can concentrate entirely on the optimal concurrency of his algorithm in the abstract. If the best-case scenario for his problem would employ 500 concurrent tasks, then he can paddle ahead and create 500 GCD queues and ration his travail among them. GCD will figure out how many actual threads to create to carry out the work. Furthermore it will adjust the number of threads dynamically as the conditions on the system change.

    But perhaps most importantly, as fresh hardware is released with more and more CPU cores, the programmer does not need to change his application at all. Thanks to GCD, it will transparently rob edge of any and every available computing resources, up to—but not past!—the optimal amount of concurrency as originally defined by the programmer when he chose how many queues to create.

    But wait, there's more! GCD queues can actually be arranged in arbitrarily tangled directed acyclic graphs. (Actually, they can be cyclic too, but then the deportment is undefined. Don't carry out that.) Queue hierarchies can be used to funnel tasks from disparate subsystems into a narrower set of centrally controlled queues, or to obligate a set of customary queues to delegate to a serial queue, effectively serializing them every indirectly.

    There are besides several levels of priority for queues, dictating how often and with what urgency threads are distributed to them from the pool. Queues can be suspended, resumed, and cancelled. Queues can besides be grouped, allowing every tasks distributed to the group to be tracked and accounted for as a unit.

    Overall, GCD's employ of queues and threads forms a simple, elegant, but besides extremely pragmatic architecture.


    Okay, so GCD is a worthy pass to do efficient employ of the available hardware. But is it really any better than BeOS's approach to multithreading? We've already seen a few ways that GCD avoids the pitfalls of BeOS (e.g., the reuse of threads and the maintenance of a global pool of threads that's correctly sized for the available hardware). But what about the problem of overwhelming the programmer by requiring threads in places where they complicate, rather than enhance the application?

    GCD embodies a philosophy that is at the opposite finish of the spectrum from BeOS's "pervasive multithreading" design. Rather than achieving responsiveness by getting every feasible component of an application running concurrently on its own thread (and paying a heavy price in terms of tangled data sharing and locking concerns), GCD encourages a much more limited, hierarchical approach: a main application thread where every the user events are processed and the interface is updated, and worker threads doing specific jobs as needed.

    In other words, GCD doesn't require developers to deem about how best to split the travail of their application into multiple concurrent threads (though when they're ready to carry out that, GCD will be willing and able to help). At its most basic level, GCD aims to hearten developers to paddle from thinking synchronously to thinking asynchronous. Something fondness this: "Write your application as usual, but if there's any piece of its operation that can reasonably be expected to rob more than a few seconds to complete, then for the adore of Zarzycki, accumulate it off the main thread!"

    That's it; no more, no less. Beach ball banishment is the cornerstone of user interface responsiveness. In some respects, everything else is gravy. But most developers know this intuitively, so why carry out they still descry the beach ball in Mac OS X applications? Why don't every applications already execute every of their potentially long-running tasks on background threads?

    A few reasons relish been mentioned already (e.g., the rigor of knowing how many threads to create) but the expansive one is much more pragmatic. Spinning off a thread and collecting its result has always been a bit of a pain. It's not so much that it's technically difficult, it's just that it's such an definite fracture from coding the actual travail of your application to coding every this task-management plumbing. And so, especially in borderline cases, fondness an operation that may rob 3 to 5 seconds, developers just carry out it synchronously and paddle onto the next thing.

    Unfortunately, there's a surprising number of very common things that an application can carry out that execute quickly most of the time, but relish the potential to rob much longer than a few seconds when something goes wrong. Anything that touches the file system may stall at the lowest levels of the OS (e.g., within blocking read() and write() calls) and be matter to a very long (or at least an "unexamined-by-the-application-developer") timeout. The same goes for cognomen lookups (e.g., DNS or LDAP), which almost always execute instantly, but trap many applications completely off-guard when they start taking their sweet time to recrudesce a result. Thus, even the most meticulously constructed Mac OS X applications can finish up throwing the beach ball in their pan from time to time.

    With GCD, Apple is adage it doesn't relish to be this way. For example, suppose a document-based application has a button that, when clicked, will analyze the current document and panoply some inquisitive statistics about it. In the common case, this analysis should execute in under a second, so the following code is used to connect the button with an action:

    - (IBAction)analyzeDocument:(NSButton *)sender { NSDictionary *stats = [myDoc analyze]; [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }

    The first line of the duty carcass analyzes the document, the second line updates the application's internal state, and the third line tells the application that the statistics view needs to be updated to reflect this fresh state. It every follows a very common pattern, and it works worthy as long as not one of these steps—which are every running on the main thread, remember—takes too long. Because after the user presses the button, the main thread of the application needs to exploit that user input as swift as feasible so it can accumulate back to the main event loop to process the next user action.

    The code above works worthy until a user opens a very great or very tangled document. Suddenly, the "analyze" step doesn't rob one or two seconds, but 15 or 30 seconds instead. Hello, beach ball. And still, the developer is likely to hem and haw: "This is really an exceptional situation. Most of my users will never open such a great file. And anyway, I really don't want to start reading documentation about threads and adding every that extra code to this simple, four-line function. The plumbing would dwarf the code that does the actual work!"

    Well, what if I told you that you could paddle the document analysis to the background by adding just two lines of code (okay, and two lines of closing braces), every located within the existing function? No application-global objects, no thread management, no callbacks, no controversy marshalling, no context objects, not even any additional variables. Behold, magnificient Central Dispatch:

    - (IBAction)analyzeDocument:(NSButton *)sender { dispatch_async(dispatch_get_global_queue(0, 0), ^{ NSDictionary *stats = [myDoc analyze]; dispatch_async(dispatch_get_main_queue(), ^{ [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }); }); }

    There's a hell of a lot of packed into those two lines of code. every of the functions in GCD initiate with dispatch_, and you can descry four such calls in the blue lines of code above. The key to the minimal invasiveness of this code is revealed in the second controversy to the two dispatch_async() calls. Thus far, I've been discussing "units of work" without specifying how, exactly, GCD models such a thing. The answer, now revealed, should appear obvious in retrospect: blocks! The ability of blocks to capture the surrounding context is what allows these GCD calls to be dropped perquisite into some existing code without requiring any additional setup or re-factoring or other contortions in service of the API.

    But the best piece of this code is how it deals with the problem of detecting when the background chore completes and then showing the result. In the synchronous code, the analyze method summon and the code to update the application panoply simply appear in the desired sequence within the function. In the asynchronous code, miraculously, this is still the case. Here's how it works.

    The outer dispatch_async() summon puts a chore on a global concurrent GCD queue. That task, represented by the secrete passed as the second argument, contains the potentially time-consuming analyze method call, plus another summon to dispatch_async() that puts a chore onto the main queue—a serial queue that runs on the main thread, remember—to update the application's user interface.

    User interface updates must every be done from the main thread in a Cocoa application, so the code in the inner secrete could not be executed anywhere else. But rather than having the background thread dispatch some kindly of special-purpose notification back to the main thread when the analyze method summon completes (and then adding some code to the application to detect and exploit this notification), the travail that needs to be done on the main thread to update the panoply is encapsulated in yet another secrete within the larger one. When the analyze summon is done, the inner secrete is save onto the main queue where it will (eventually) rush on the main thread and carry out its travail of updating the display.

    Simple, elegant, and effective. And for developers, no more excuses.

    Believe it or not, it's just as simple to rob a serial implementation of a sequence of independent operations and parallelize it. The code below does travail on weigh elements of data, one after the other, and then summarizes the results once every the elements relish been processed.

    for (i = 0; i < count; i++) { results[i] = do_work(data, i); } total = summarize(results, count);

    Now here's the parallel version which puts a separate chore for each ingredient onto a global concurrent queue. (Again, it's up to GCD to resolve how many threads to actually employ to execute the tasks.)

    dispatch_apply(count, dispatch_get_global_queue(0, 0), ^(size_t i) { results[i] = do_work(data, i); }); total = summarize(results, count);

    And there you relish it: a for loop replaced with a concurrency-enabled equivalent with one line of code. No preparation, no additional variables, no impossible decisions about the optimal number of threads, no extra travail required to wait for every the independent tests to complete. (The dispatch_apply() summon will not recrudesce until every the tasks it has dispatched relish completed.) Stunning.

    Grand Central Awesome

    Of every the APIs added in Snow Leopard, magnificient Central Dispatch has the most far-reaching implications for the future of Mac OS X. Never before has it been so simple to carry out travail asynchronously and to spread workloads across many CPUs.

    When I first heard about magnificient Central Dispatch, I was extremely skeptical. The greatest minds in computer science relish been working for decades on the problem of how best to extract parallelism from computing workloads. Now here was Apple apparently promising to unravel this problem. Ridiculous.

    But magnificient Central Dispatch doesn't actually address this issue at all. It offers no assist whatsoever in deciding how to split your travail up into independently executable tasks—that is, deciding what pieces can or should be executed asynchronously or in parallel. That's still entirely up to the developer (and still a tough problem). What GCD does instead is much more pragmatic. Once a developer has identified something that can be split off into a separate task, GCD makes it as simple and non-invasive as feasible to actually carry out so.

    The employ of FIFO queues, and especially the being of serialized queues, seems counter to the spirit of ubiquitous concurrency. But we've seen where the Platonic example of multithreading leads, and it's not a pleasant residence for developers.

    One of Apple's slogans for magnificient Central Dispatch is "islands of serialization in a sea of concurrency." That does a worthy job of capturing the practical reality of adding more concurrency to run-of-the-mill desktop applications. Those islands are what seclude developers from the thorny problems of simultaneous data access, deadlock, and other pitfalls of multithreading. Developers are encouraged to identify functions of their applications that would be better executed off the main thread, even if they're made up of several sequential or otherwise partially interdependent tasks. GCD makes it simple to fracture off the entire unit of travail while maintaining the existing order and dependencies between subtasks.

    Those with some multithreaded programming experience may be unimpressed with the GCD. So Apple made a thread pool. expansive deal. They've been around forever. But the angels are in the details. Yes, the implementation of queues and threads has an elegant simplicity, and baking it into the lowest levels of the OS really helps to lower the perceived barrier to entry, but it's the API built around blocks that makes magnificient Central Dispatch so attractive to developers. Just as Time Machine was "the first backup system people will actually use," magnificient Central Dispatch is poised to finally spread the heretofore shadowy expertise of asynchronous application design to every Mac OS X developers. I can't wait.

    OpenCL Somehow, OpenCL got in on the <a href="">"core" branding</a>Somehow, OpenCL got in on the "core" branding

    So far, we've seen a few examples of doing more with more: a new, more modern compiler infrastructure that supports an well-known fresh language feature, and a powerful, pragmatic concurrency API built on top of the fresh compilers' uphold for said language feature. every this goes a long pass towards helping developers and the OS itself do maximum employ of the available hardware.

    But CPUs are not the only components experiencing a glut of transistors. When it comes to the proliferation of independent computation engines, another piece of silicon inside every Mac is the undisputed title holder: the GPU.

    The numbers divulge the tale. While Mac CPUs accommodate up to four cores (which may exhibit up as eight rational cores thanks to symmetric multithreading), high-end GPUs accommodate well over 200 processor cores. While CPUs are just now edging over 100 GFLOPS, the best GPUs are capable of over 1,000 GFLOPS. That's one trillion floating-point operations per second. And fondness CPUs, GPUs now approach more than one on a board.

    Writing for the GPU

    Unfortunately, the cores on a GPU are not general-purpose processors (at least not yet). They're much simpler computing engines that relish evolved from the fixed-function silicon of their ancestors that could not be programmed directly at all. They don't uphold the loaded set of instructions available on CPUs, the maximum size of the programs that will rush is often limited and very small, and not every of the features of the industry-standard IEEE floating-point computation specification are supported.

    Today's GPUs can be programmed, but the most common forms of programmability are still firmly planted in the world of graphics programming: vertex shaders, geometry shaders, pixel shaders. Most of the languages used to program GPUs are similarly graphically focused: HLSL, GLSL, Cg.

    Nevertheless, there are computational tasks outside the realm of graphics that are a noble fit for GPU hardware. It would be nice if there were a non-graphics-oriented language to write them in. Creating such a thing is quite a challenge, however. GPU hardware varies wildly in every imaginable way: number and type of execution units, available data formats, instruction sets, remembrance architecture, you cognomen it. Programmers don't want to be exposed to these differences, but it's difficult to travail around the complete lack of a feature or the unavailability of a particular data type.

    GPU vendor NVIDIA gave it a shot, however, and produced CUDA: a subset of the C language with extensions for vector data types, data storage specifiers that reflect typical GPU remembrance hierarchy, and several bundled computational libraries. CUDA is but one entrant in the burgeoning GPGPU realm (General-Purpose computing on Graphics Processing Units). But coming from a GPU vendor, it faces an uphill battle with developers who really want a vendor-agnostic solution.

    In the world of 3D programming, OpenGL fills that role. As you've surely guessed by now, OpenCL aims to carry out the same for general-purpose computation. In fact, OpenCL is supported by the same consortium as OpenGL: the ominously named Khronos Group. But do no mistake, OpenCL is Apple's baby.

    Apple understood that OpenCL's best desultory of success was to become an industry standard, not just an Apple technology. To do that happen, Apple needed the cooperation of the top GPU vendors, plus an agreement with an established, widely-recognized standards body. It took a while, but now it's every approach together.

    OpenCL is a lot fondness CUDA. It uses a C-like language with the vector extensions, it has a similar model of remembrance hierarchy, and so on. This is no surprise, considering how closely Apple worked with NVIDIA during the development of OpenCL. There's besides no pass any of the expansive GPU vendors would radically alter their hardware to uphold an as-yet-unproven standard, so OpenCL had to travail well with GPUs already designed to uphold CUDA, GLSL, and other existing GPU programming languages.

    The OpenCL difference

    This is every well and good, but to relish any impact on the day-to-day life of Mac users, developers actually relish to employ OpenCL in their applications. Historically, GPGPU programming languages relish not seen much employ in traditional desktop applications. There are several reasons for this.

    Early on, writing programs for the GPU often required the employ of vendor-specific assembly languages that were far removed from the experience of writing a typical desktop application using a concurrent GUI API. The more C-like languages that came later remained either graphics-focused, vendor-specific, or both. Unless running code on the GPU would accelerate a core component of an application by an order of magnitude, most developers still could not be bothered to navigate this alien world.

    And even if the GPU did give a huge hasten boost, relying on graphics hardware for general-purpose computation was very likely to narrow the potential audience for an application. Many older GPUs, especially those organize in laptops, cannot rush languages fondness CUDA at all.

    Apple's key conclusion in the design of OpenCL was to allow OpenCL programs to rush not just on GPUs, but on CPUs as well. An OpenCL program can query the hardware it's running on and enumerate every eligible OpenCL devices, categorized as CPUs, GPUs, or dedicated OpenCL accelerators (the IBM Cell Blade server—yes, that Cell—is apparently one such device). The program can then dispatch its OpenCL tasks to any available device. It's besides feasible to create a solitary rational device consisting of any combination of eligible computing resources: two GPUs, a GPU and two CPUs, etc.

    The advantages of being able to rush OpenCL programs on both CPUs and GPUs are obvious. Every Mac running Snow Leopard, not just those with the recent-model GPUs, can rush a program that contains OpenCL code. But there's more to it than that.

    Certain kinds of algorithms actually rush faster on high-end multi-core CPUs than on even the very fastest available GPUs. At WWDC 2009, an engineer from Electronic Arts demonstrated an OpenCL port of a skinning engine from one of its games running over four times faster on a four-core Mac Pro than on an NVIDIA GeForce GTX285. Restructuring the algorithm and making many other changes to better suit the limitations (and strengths) of the GPU pushed it back ahead of the CPU by a wide margin, but sometimes you just want the system you relish to rush well as-is. Being able to target the CPU is extremely useful in those cases.

    Moreover, writing vector code for Intel CPUs "the old-fashioned way" can be a actual pain. There's MMX, SSE, SSE2, SSE3, and SSE4 to deal with, every with slightly different capabilities, and every of which obligate the programmer to write code fondness this:

    r1 = _mm_mul_ps(m1, _mm_add_ps(x1, x2));

    OpenCL's indigenous uphold for vector types de-clutters the code considerably:

    r1 = m1 * (x1 + x2);

    Similarly, OpenCL's uphold for implicit parallelism makes it much easier to rob edge of multiple CPU cores. Rather than writing every the logic to split your data into pieces and ration those pieces to the parallel-computing hardware, OpenCL lets you write just the code to operate on a solitary piece of the data and then dispatch it, along with the entire secrete of data and the desired even of parallelism, to the computing device.

    This arrangement is taken for granted in traditional graphics programming, where code implicitly works on every pixels in a texture or every vertices in a polygon; the programmer only needs to write code that will exist in the "inner loop," so to speak. An API with uphold for this kindly of parallelism that runs on CPUs as well as GPUs fills an well-known gap.

    Writing to OpenCL besides future-proofs task- or data-parallel code. Just as the same OpenGL code will accumulate faster and faster as newer, more powerful GPUs are released, so too will OpenCL code fulfill better as CPUs and GPUs accumulate faster. The extra layer of abstraction that OpenCL provides makes this possible. For example, though vector code written several years ago using MMX got faster as CPU clock speeds increased, a more significant performance boost likely requires porting the code to one of the newer SSE instruction sets.

    As newer, more powerful vector instruction sets and parallel hardware becomes available, Apple will update its OpenCL implementations to rob edge of them, just as video card makers and OS vendors update their OpenGL drivers to rob edge of faster GPUs. Meanwhile, the application developer's code remains unchanged. Not even a recompile is required.

    Here be dragons (and trains)

    How, you may wonder, can the same compiled code finish up executing using SSE2 on one machine and SSE4 on another, or on an NVIDIA GPU on one machine and an ATI GPU on another? To carry out so would require translating the device-independent OpenCL code to the instruction set of the target computing device at runtime. When running on a GPU, OpenCL must besides ship the data and the newly translated code over to the video card and collect the results at the end. When running on the CPU, OpenCL must sort for the requested even of parallelism by creating and distributing threads appropriately to the available cores.

    Well, wouldn't you know it? Apple just happens to relish two technologies that unravel these exact problems.

    Want to compile code "just in time" and ship it off to a computing device? That's what LLVM was born to do—and, indeed, what Apple did with it in Leopard, albeit on a more limited scale. OpenCL is a natural extension of that work. LLVM allows Apple to write a solitary code generator for each target instruction set, and concentrate every of its effort on a solitary device-independent code optimizer. There's no longer any need to duplicate these tasks, using one compiler to create the static application executable and having to jury-rig another for just-in-time compilation.

    (Oh, and by the way, remember Core Image? That's another API that needs to compile code just-in-time and ship it off to execute on parallel hardware fondness GPUs and multi-core CPUs. In Snow Leopard, Core Image has been re-implemented using OpenCL, producing a hefty 25% overall performance boost.)

    To exploit chore parallelism and provision threads, OpenCL is built on top of magnificient Central Dispatch. This is such a natural fit that it's a bit surprising that the OpenCL API doesn't employ blocks. I deem Apple decided that it shouldn't press its luck when it comes to getting its home-grown technologies adopted by other vendors. This conclusion already seems to be paying off, as AMD has its own OpenCL implementation under way.

    The top of the pyramid

    Though the underlying technologies, Clang, blocks and magnificient Central Dispatch, will undoubtedly be more widely used by developers, OpenCL represents the culmination of that particular technological thread in Snow Leopard. This is the gold benchmark of software engineering: creating a fresh public API by edifice it on top of lower-level, but equally well-designed and implemented public APIs.

    A unified abstraction for the ever-growing heterogeneous collection of parallel computing silicon in desktop computers was sorely needed. We've got an increasing population of powerful CPU cores, but they still exist in numbers that are orders of magnitude lower than the hundreds of processing units in modern GPUs. On the other hand, GPUs still relish a ways to paddle to trap up with the power and flexibility of a full-fledged CPU core. But even with every the differences, writing code exclusively for either one of those worlds still smacks of leaving money on the table.

    With OpenCL in hand, there's no longer a need to save every your eggs in one silicon basket. And with the advent of hybrid CPU/GPU efforts fondness Intel's Larabee, which employ CPU-caliber processing engines, but in much higher numbers, OpenCL may prove even more well-known in the coming years.

    Transistor harvest

    Collectively, the concurrency-enabling features introduced in Snow Leopard represent the biggest boost to asynchronous and parallel software development in any Mac OS X release—perhaps in any desktop operating system release ever. It may be arduous for end-users to accumulate excited about "plumbing" technologies fondness magnificient Central Dispatch and OpenCL, let lonesome compilers and programming language features, but it's upon these foundations that developers will create ever-more-impressive edifices of software. And if those applications tower over their synchronous, serial predecessors, it will be because they stand on the shoulders of giants.

    QuickTime Player's  fresh icon (Not a fan)QuickTime Player's fresh icon (Not a fan) QuickTime Player

    There's been some confusion surrounding QuickTime in Snow Leopard. The earlier section about QuickTime X explains what you need to know about the present and future of QuickTime as a technology and an API. But a few of Apple's decisions—and the extremely overloaded import of the word "QuickTime" in the minds of consumers—have blurred the picture somewhat.

    The first head-scratcher occurs during installation. If you occur to click on the "Customize…" button during installation, you'll descry the following options:

    QuickTime 7 is an optional install?QuickTime 7 is an optional install?

    We've already talked about Rosetta being an optional install, but QuickTime 7 too? Isn't QuickTime severely crippled without QuickTime 7? Why in the world would that be an optional install?

    Well, there's no need to panic. That detail in the installer should actually read "QuickTime Player 7." QuickTime 7, the mature but extremely capable media framework discussed earlier, is installed by default in Snow Leopard—in fact, it's mandatory. But the player application, the one with the mature blue "Q" icon, the one that many casual users actually deem of as being "QuickTime," that's been replaced with a fresh QuickTime-X-savvy version sporting a pudgy fresh icon (see above right).

    The fresh player application is a expansive departure from the old. Obviously, it leverages QuickTime X for more efficient video playback, but the user interface is besides completely new. Gone are the gray rim and bottom-mounted playback controls from the mature QuickTime Player, replaced by a frameless window with a black title bar and a floating, moveable set of controls.

    The  fresh QuickTime Player: boldly going where <a href="">NicePlayer</a> has gone before Enlarge / The fresh QuickTime Player: boldly going where NicePlayer has gone before

    It's fondness a combination of the window treatment of the excellent NicePlayer application and the full-screen playback controls from the mature QuickTime Player. I'm a bit bothered by two things. First, the ever-so-slightly clipped corners appear fondness a harmful idea. Am I just putative to give up those dozen-or-so pixels? NicePlayer does it right, showing crisp, square corners.

    Second, the floating playback controls obscure the movie. What if I'm scrubbing around looking for something in that piece of the frame? Yes, you can paddle the controls, but what if I'm looking for something in an unknown location in the frame? Also, the title bar obscures an entire swath of the top of the frame, and this can't be moved. I appreciate the compactness of this approach, but it'd be nice if the title bar overlap could be disabled and the controls could be dragged off the movie entirely and docked to the bottom or something.

    (One blessing for people who partake my OCD tendencies: if you paddle the floating controls, they don't remember their position the next time you open a movie. Why is that a blessing? Because if it worked the other way, we'd every expend pass too much time fretting about their inability to restore the controller to its default, precisely centered position. Sad, but true.)

    The fresh QuickTime Player presents a decidedly iMovie-like (or is it iPhone-like, nowadays?) interface for trimming video. Still-frame thumbnails are placed side-by-side to contour a timeline, with adjustable stops at each finish for trimming.

    Trimming in the  fresh QuickTime Player Enlarge / Trimming in the fresh QuickTime Player

    Holding down the option key changes from a thumbnail timeline to an audio waveform display:

    Trimming with audio waveform view Enlarge / Trimming with audio waveform view

    In both the video and audio cases, I relish to miracle exactly how useful the fancy timeline appearances are. The audio waveform is quite small and compressed, and the limited horizontal space of the in-window panoply means a movie can only exhibit a handful of video frames in its timeline. Also, if there's any ability to carry out fine adjustments using something other than extremely observant mouse movements (which are necessarily matter to a limited resolution) then I couldn't find it. Final gash Pro this is not.

    QuickTime Player has learned another fresh trick: screen recording. The controls are limited, so more demanding users will still relish a need for a full-featured screen recorder, but QuickTime Player gets the job done.

    Screen recording in QuickTime PlayerScreen recording in QuickTime Player

    There's besides an audio-only option, with a similarly simplified collection of settings.

    Audio recordingAudio recording

    Finally, the fresh QuickTime Player has the ability to upload a movie directly to YouTube and MobileMe, dispatch one via e-mail, or add it to your iTunes library. The export options are besides vastly simplified, with preset options for iPhone/iPod, Apple TV, and HD 480p and 720p.

    Unfortunately, the list of things you can't carry out with the fresh QuickTime Player is quite long. You can't cut, copy, and paste whimsical portions of a movie (trimming only affects the ends); you can't extract or delete individual tracks or overlay one track onto another (optionally scaling to fit); you can't export a movie by choosing from the replete set of available QuickTime audio and video codecs. every of these things were feasible with the mature QuickTime Player—if, that is, you paid the $30 for a QuickTime Pro license. In the past, I've described this extra fee as "criminally stupid", but the features it enabled in QuickTime Player were really useful.

    It's tempting to attribute their absence in the fresh QuickTime Player to the previously discussed limitations of QuickTime X. But the fresh QuickTime Player is built on top of QTKit, which serves as a front-end for both QuickTime X and QuickTime 7. And it does, after all, feature some limited editing features fondness trimming, plus some previously "Pro"-only features fondness full-screen playback. Also, the fresh QuickTime Player can indeed play movies using third-party plug-ins—a feature clearly powered by QuickTime 7.

    Well, Snow Leopard has an extremely pleasant flabbergast waiting for you if you install the optional QuickTime Player 7. When I did so, what I got was the mature QuickTime Player—somewhat insultingly installed in the "Utilities" folder—with every of its "Pro" features permanently unlocked. Yes, the tyranny of QuickTime Pro seems to be at an end…

    QuickTime Pro: now free for everyone?QuickTime Pro: now free for everyone?

    …but perhaps the key word above is "seems," because QuickTime Player 7 does not relish every "pro" features unlocked for everyone. I installed Snow Leopard onto an vacant disk, and QuickTime 7 was not automatically installed (as it is when the installer detects an existing QuickTime Pro license on the target disk). After booting from my fresh Snow Leopard volume, I manually installed the "QuickTime 7" optional component using the Snow Leopard installer disk.

    The result for me was a QuickTime Player 7 application with every pro features unlocked and with no visible QuickTime Pro registration information. I did, however, relish a QuickTime Pro license on one of the attached drives. Apparently, the installer detected this and gave me an unlocked QuickTime Player 7 application, even though the boot volume never had a QuickTime Pro license on it.

    The Dock

    The fresh appearance of some aspects of the Dock are accompanied by some fresh functionality as well. Clicking and holding on a running application's Dock icon now triggers Expos�, but only for the windows belonging to that application. Dragging a file onto a docked application icon and holding it there for a bit produces the same result. You can then continue that same drag onto one of the Exposé window thumbnails and hover there a bit to bring that window to the front and drop the file into it. It's a pretty handy technique, once you accumulate in the usage of doing it.

    The Exposé panoply itself is besides changed. Now, minimized windows are displayed in smaller contour on the bottom of the screen below a thin line.

    Dock Exposé with  fresh placement of minimized windows Enlarge / Dock Exposé with fresh placement of minimized windows

    In the screenshot above, you'll notice that not one of the minimized windows appear in my Dock. That's thanks to another welcome addition: the ability to minimize windows "into" the application icon. You'll find the setting for this in the Dock's preference pane.

    New Dock preference: Minimize windows into application iconNew Dock preference: Minimize windows into application icon Minimized windows in a Dock application menuMinimized window denoted by a diamond

    Once set, minimized windows will slip behind the icon of their parent application and then disappear. To accumulate them back, either right-click the application icon (see right) or trigger Exposé.

    The Dock's grid view for folders now incorporates a scroll bar when there are too many items to fit comfortably. Clicking on a folder icon in the grid now shows that folder's contents within the grid, allowing you to navigate down several folders to find a buried item. A small "back" navigation button appears once you descend.

    These are every useful fresh behaviors, and quite a premium considering the putative "no fresh features" stance of Snow Leopard. But the fundamental nature of the Dock remains the same. Users who want a more resilient or more powerful application launcher/folder organizer/window minimization system must still either sacrifice some functionality (e.g., Dock icon badges and bounce notifications) or continue to employ the Dock in addition to a third-party application.

    The option to maintain minimized windows from cluttering up the Dock was long overdue. But my enthusiasm is tempered by my frustration at the continued inability to click on a docked folder and relish it open in the Finder, while besides retaining the ability to drag items into that folder. This was the default deportment for docked folders for the first six years of Mac OS X's life, but it changed in Leopard. Snow Leopard does not better matters.

    Docking an alias to a folder provides the single-click-open behavior, but items cannot be dragged into a docked folder alias for some inexplicable reason. (Radar 5775786, closed in March 2008 with the terse explanation, "not currently supported.") Worse, dragging an detail to a docked folder alias looks fondness it will travail (the icon highlights) but upon release, the dragged detail simply springs back to its original location. I really hoped this one would accumulate fixed in Snow Leopard. No such luck.

    Dock grid view's in-place navigation with back buttonDock grid view's in-place navigation with back button The Finder

    One of the earliest leaked screenshots of Snow Leopard included an innocuous-looking "Get Info…" window for the Finder, presumably to exhibit that its version number had been updated to 10.6. The more inquisitive tidbit of information it revealed was that the Finder in Snow Leopard was a 64-bit application.

    The Mac OS X Finder started its life as the designated "dog food" application for the Carbon backward-compatibility API for Mac OS X. Over the years, the Finder has been a frequent target of dissatisfaction and scorn. Those harmful feelings frequently spilled over into the parallel debate over API supremacy: Carbon vs. Cocoa.

    "The Finder sucks because it's a Carbon app. What they need is a Cocoa Finder! Surely that will unravel every their woes." Well, Snow Leopard features a 64-bit Finder, and as they every know, Carbon was not ported to 64-bit. Et voila! A Cocoa Finder in Snow Leopard. (More on the woes in a bit.)

    The conversion to Cocoa followed the Snow Leopard formula: no fresh features… except for maybe one or two. And so, the "new" Cocoa Finder looks and works almost exactly fondness the mature Carbon Finder. The biggest indicator of its "Cocoa-ness" is the extensive employ of Core Animation transitions. For example, when a Finder window does its schizophrenic transformation from a sidebar-bedecked browser window to its minimally-adorned form, it no longer happens in a blink. Instead, the sidebar slides away and fades, the toolbar shrinks, and everything tucks in to contour its fresh shape.

    Despite crossing the line in a few cases, the Core Animation transitions carry out do the application feel more polished, and yes, "more Cocoa." And presumably the employ of Cocoa made it so darn simple to add features that the developers just couldn't resist throwing in a few.

    The number-one feature request from heavy column-view users has finally been implemented: sortable columns. The sort order applies to every columns at once, which isn't as nice as per-column sorting, but it's much better than nothing at all. The sort order can be set using a menu command (each of which has a keyboard shortcut) or by right-clicking in an unoccupied region of a column and selecting from the resulting context menu.

    Column view sorting context menu Enlarge / Column view sorting context menu Column view sorting menu Enlarge / Column view sorting menu

    Even the lowly icon view has been enhanced in Snow Leopard. Every icon-view window now includes a small slider to control the size of the icons.

    The Finder's icon view with its  fresh slider controlThe Finder's icon view with its fresh slider control

    This may appear a bit odd—how often carry out people change icon sizes?—but it makes much more sense in the context of previewing images in the Finder. This employ case is made even more apposite by the recent expansion of the maximum icon size to 512x512 pixels.

    The icon previews themselves relish been enhanced to better match the abilities available in Quick Look. save it every together and you can smoothly zoom a small PDF icon, for example, into the impressively high-fidelity preview shown below, complete with the ability to spin pages. One press of the space bar and you'll progress to the even larger and more resilient Quick glance view. It's a pretty smooth experience.

    Not your father's icon: 512x512 pixels of multi-page PDF previewingNot your father's icon: 512x512 pixels of multi-page PDF previewing

    QuickTime previews relish been similarly enhanced. As you zoom in on the icon, it transforms into a miniature movie player, adorned with an odd circular progress indicator. Assuming users are willing to wrangle with the vagaries of the Finder's view settings successfully enough to accumulate icon view to stick for the windows where it's most useful, I deem that odd limited slider is actually going to accumulate a lot of use.

    The Finder's QuickTime preview. (The "glare" overlay is a bit much.)The Finder's QuickTime preview. (The "glare" overlay is a bit much.)

    List view besides has a few enhancements—accidental, incidental, or otherwise. The drag region for each list view detail now spans the entire line. In Leopard, though the entire line was highlighted, only the file cognomen or icon portion could be dragged. Trying to drag anywhere else just extended the selection to other items in the list view as the cursor was moved. I'm not positive whether this change in deportment is intentional or if it's just an unexamined consequence of the underlying control used for list view in the fresh Cocoa Finder. Either way, thumbs up.

    Double-clicking on the dividing line between two column headers in list view will "right-size" that column. For most columns, this means expanding or shrinking to minimally fit the widest value in the column. Date headers will progressively shrink to exhibit less verbose date formats. Supposedly, this worked intermittently in Leopard as well. But whether Cocoa is bringing this feature for the first time or is just making it travail correctly for the first time, it's a change for the better.

    Searching using the Finder's browser view is greatly improved by the implementation of one of those limited things that many users relish been clamoring for year after year. There's now a preference to select the default scope of the search realm in the Finder window toolbar. Can I accumulate an amen?

    Default Finder search location: configurable at last.Default Finder search location: configurable at last.

    Along similar lines, there are other long-desired enhancements that will paddle a long pass towards making the desktop environment feel more solid. A noble sample is the improved handling of the dreaded "cannot eject, disk in use" error. The obvious follow-up question from the user is, "Okay, so what's using it?" Snow Leopard finally provides that information.

    No more guessingNo more guessing

    (Yes, Mac OS X will rebuff to eject a disk if your current working directory in a command-line shell is on that disk. kindly of cool, but besides kindly of annoying.)

    Another feasible user response to a disk-in-use error is, "I don't care. I'm in a hurry. Just eject it!" That's an option now as well.

    Forcible ejection in progressForcible ejection in progress

    Hm, but why did I accumulate information about the offending application in one dialog, an option to obligate ejection in the other, but neither one presented both choices? It's a mystery to me, but presumably it's related to exactly what information the Finder has about the contention for the disk. (As always, the lsof command is available if you want to figure it out the old-fashioned way.)


    So does the fresh Cocoa Finder finally deport every of those embarrassing bugs from the bad-old days of Carbon? Not quite. This is essentially the "1.0" release of the Cocoa Finder, and it has its partake of 1.0 bugs. Here's one discovered by Glen Aspeslagh (see image right).

    Do you descry it? If not, glance closer at the order of the dates in the supposedly sorted "Date Modified" column. So yeah, that mature Finder magic has not been entirely extinguished.

    There besides remains some weirdness in the operation of the icon grid. In a view where grid snap is turned on (or is enabled transiently by holding down the command key during a drag) icons appear terrified of each other, leaving huge distances between themselves and their neighbors when they select which grid spot to snap to. It's as if the Finder lives in mortal apprehension that one of these files will someday accumulate a 200-character filename that will overlap with a neighboring file's name.

    The worst incarnation of this deportment happens along the perquisite edge of the screen where mounted volumes appear on the desktop. (Incidentally, this is not the default; if you want to descry disks on your desktop, you must enable this preference in the Finder.) When I mount a fresh disk, I'm often surprised to descry where it ends up appearing. If there are any icons remotely immediate to the perquisite edge of the screen, the disk icon will rebuff to appear there. Again, the Finder is not avoiding any actual cognomen or icon overlapping. It appears to be avoiding the mere possibility of overlapping at some unspecified point in the future. Silly.

    Finder report card

    Overall, the Snow Leopard Finder takes several significant steps forward—64-bit/Cocoa future-proofing, a few new, useful features, added polish—and only a few shuffles backwards with the slight overuse of animation and the continued presence of some puzzling bugs. Considering how long it took the Carbon Finder to accumulate to its pre-Snow-Leopard feature set and even of polish, it's quite an achievement for a Cocoa Finder to match or exceed its predecessor in its very first release. I'm positive the Carbon vs. Cocoa warriors would relish had a realm day with that statement, were Carbon not save out to pasture in Leopard. But it was, and to the victor paddle the spoils.


    Snow Leopard's headline "one fresh feature" is uphold for Microsoft Exchange. This appears to be, at least partially, yet another hand-me-down from the iPhone, which gained uphold for Exchange in its 2.0 release and expanded on it in 3.0. Snow Leopard's Exchange uphold is weaved throughout the expected crop of applications in Mac OS X: iCal, Mail, and Address Book.

    The expansive caveat is that it will only travail with a server running Exchange 2007 (Service Pack 1, Update Rollup 4) or later. While I'm positive Microsoft greatly appreciates any additional upgrade revenue this conclusion provides, it means that for users whose workplaces are still running older versions of Exchange, Snow Leopard's "Exchange support" might as well not exist.

    Those users are probably already running the only other viable Mac OS X Exchange client, Microsoft Entourage, so they'll likely just sit taut and wait for their IT departments to upgrade. Meanwhile, Microsoft is already making overtures to these users with the promised creation—finally—of an honest-to-goodness version of Outlook for Mac OS X.

    In my admittedly brief testing, Snow Leopard's Exchange uphold seems to travail as expected. I had to relish one of the Microsoft mavens in the Ars Orbiting HQ spin up an Exchange 2007 server just for the purposes of this review. However it was configured, every I had to enter in the Mail application was my replete name, e-mail address, and password, and it automatically discovered every apposite settings and configured iCal and Address book for me.

    Exchange setup: surprisingly easyExchange setup: surprisingly easy

    Windows users are no doubt accustomed to this kindly of Exchange integration, but it's the first time I've seen it on the Mac platform—and that includes my many years of using Entourage.

    Access to Exchange-related features is decidedly subdued, in keeping with the existing interfaces for Mail, iCal, and Address Book. If you're expecting the swarm of panels and toolbar buttons organize in Outlook on Windows, you're in for a bit of a shock. For example, here's the "detail" view of a meeting in iCal.

    iCal event detailiCal event detail

    Clicking the "edit" button hardly reveals more.

    Event editor: that's it?Event editor: that's it?

    The "availability" window besides includes the bare minimum number of controls and displays to accumulate the job done.

    Meeting availability checker Enlarge / Meeting availability checker

    The integration into Mail and Address book is even more subtle—almost entirely transparent. This is to be construed as a feature, I suppose. But though I don't know enough about Exchange to be completely sure, I can't shake the sentiment that there are Exchange features that remain inaccessible from Mac OS X clients. For example, how carry out I book a "resource" in a meeting? If there's a pass to carry out so, I couldn't ascertain it.

    Still, even basic Exchange integration out-of-the-box goes long pass towards making Mac OS X more welcome in corporate environments. It remains to be seen how convinced IT managers are of the "realness" of Snow Leopard's Exchange integration. But I've got to deem that being able to dispatch and receive mail, create and respond to meeting invitations, and employ the global corporate address book is enough for any Mac user to accumulate along reasonably well in an Exchange-centric environment.


    The thing is, there's not really much to squawk about performance in Snow Leopard. Dozens of benchmark graphs lead to the same simple conclusion: Snow Leopard is faster than Leopard. Not shockingly so, at least in the aggregate, but it's faster. And while isolating one particular subsystem with a micro-benchmark may betray some impressive numbers, it's the pass these small changes combine to better the real-world experience of using the system that really makes a difference.

    One sample Apple gave at WWDC was making an initial Time Machine backup over the network to a Time Capsule. Apple's approach to optimizing this operation was to address each and every subsystem involved.

    Time Machine itself was given uphold for overlapping i/o. Spotlight indexing, which happens on Time Machine volumes as well, was identified as another time-consuming chore involved in backups, so its performance was improved. The networking code was enhanced to rob edge of hardware-accelerated checksums where possible, and the software checksum code was hand-tuned for maximum performance. The performance of HFS+ journaling, which accompanies each file system metadata update, was besides improved. For Time Machine backups that write to disk images rather than indigenous HFS+ file systems, Apple added uphold for concurrent access to disk images. The amount of network traffic produced by AFP during backups has besides been reduced.

    All of this adds up to a respectable 55% overall improvement in the hasten of an initial Time Machine backup. And, of course, the performance improvements to the individual subsystems profit every applications that employ them, not just Time Machine.

    This holistic approach to performance improvement is not likely to knock anyone's socks off, but every time you rush across a piece of functionality in Snow Leopard that disproportionately benefits from one of these optimized subsystems, it's a pleasure.

    For example, Snow Leopard shuts down and restarts much faster than Leopard. I'm not talking about boot time; I connote the time between the selection of the Shutdown or Restart command and when the system turns off or begins its fresh boot cycle. Leopard doesn't rob long at every to carry out this; only a few dozen of seconds when there are no applications open. But in Snow Leopard, it's so swift that I often thought the operating system had crashed rather than shut down cleanly. (That's actually not too far from the truth.)

    The performance boosts offered by earlier major releases of Mac OS X still dwarf Snow Leopard's speedup, but that's mostly because Mac OS X was so excruciatingly sluggish in its early years. It's simple to create a expansive performance delta when you're starting from something abysmally slow. The fact that Snow Leopard achieves consistent, measurable improvements over the already-speedy Leopard is every the more impressive.

    And yes, for the seventh consecutive time, a fresh release of Mac OS X is faster on the same hardware than its predecessor. (And for the first time ever, it's smaller, too.) What more can you inquire of for, really? Even that mature performance bugaboo, window resizing, has been completely vanquished. Grab the corner of a fully-populated iCal window—the worst-case scenario for window resizing in the mature days—and shake it as swift as you can. Your cursor will never be more than a few millimeters from the window's grab handle; it tracks your frantic motion perfectly. On most Macs, this is actually uniform in Leopard as well. It just goes to exhibit how far Mac OS X has approach on the performance front. These days, they every just rob it for granted, which is exactly the pass it should be.

    Grab bag

    In the "grab bag" section, I usually examine smaller, mostly unrelated features that don't warrant full-blown sections of their own. But when it comes to user-visible features, Snow Leopard is kindly of "all grab bag," if you know what I mean. Apple's even got its own incarnation in the contour of a giant webpage of "refinements." I'll probably overlap with some of those, but there'll be a few fresh ones here as well.

    New columns in open/save dialogs

    The list view in open and save dialog boxed now supports more than just "Name" and "Date Modified" columns. Right-click on any column to accumulate a preference of additional columns to display. I've wanted this feature for a long time, and I'm cheerful someone finally had time to implement it.

    Configurable columns in open/save dialogsConfigurable columns in open/save dialogs Improved scanner support

    The bundled Image Capture application now has the ability to talk to a wide orbit of scanners. I plugged in my Epson Stylus CX7800, a device that previously required the employ of third-party software in order to employ the scanning feature, and Image Capture detected it immediately.

    Epson scanner + Image Capture - Epson software Enlarge / Epson scanner + Image Capture - Epson software

    Image Capture is besides not a harmful limited scanning application. It has pretty noble automatic expostulate detection, including uphold for multiple objects, obviating the need to manually crop items. Given the sometimes-questionable attribute of third-party printer and scanner drivers for Mac OS X, the ability to employ a bundled application is welcome.

    System Preferences bit wars

    System Preferences, fondness virtually every other applications in Snow Leopard, is 64-bit. But since 64-bit applications can't load 32-bit plug-ins, that presents a problem for the existing crop of 32-bit third-party preference panes. System Preferences handles this situation with a reasonable amount of grace. On launch, it will panoply icons for every installed preference panes, 64-bit or 32-bit. But if you click on a 32-bit preference pane, you'll be presented with a notification fondness this:

    64-bit application vs. 32-bit plug-in: fight!64-bit application vs. 32-bit plug-in: fight!

    Click "OK" and System Preferences will relaunch in 32-bit mode, which is conveniently indicated in the title bar. Since every of the first-party preference panes are compiled for both 64-bit and 32-bit operation, System Preferences does not need to relaunch again for the duration of its use. This raises the question, why not relish System Preferences launch in 32-bit mode every the time? I suspect it's just another pass for Apple to "encourage" developers to build 64-bit-compatible binaries.

    Safari plug-ins

    The inability of of 64-bit applications load 32-bit plug-ins is a problem for Safari as well. Plug-ins are so well-known to the Web experience that relaunching in 32-bit mode is not really an option. You'd probably need to relaunch as soon as you visited your first webpage. But Apple does want Safari to rush in 64-bit mode due to some significant performance enhancements in the JavaScript engine and other areas of the application that are not available in 32-bit mode.

    Apple's solution is similar to what it did with QuickTime X and 32-bit QuickTime 7 plug-ins. Safari will rush 32-bit plug-ins in separate 32-bit processes as needed.

    Separate processes for 32-bit Safari plug-insSeparate processes for 32-bit Safari plug-ins

    This has the added, extremely significant profit of isolating potentially buggy plug-ins. According to the automated crash reporting built into Mac OS X, Apple has said that the number one reason of crashes is Web browser plug-ins. That's not the number one reason of crashes in Safari, irony you, it's the number one reason when considering every crashes of every applications in Mac OS X. (And though it was not mentioned by name, I deem they every know the primary culprit.)

    As you can descry above, the QuickTime browser plug-in gets the same treatment as gleam and other third-party 32-bit Safari plug-ins. every of this means that when a plug-in crashes, Safari in Snow Leopard does not. The window or tab containing the crashing plug-in doesn't even close. You can simply click the reload button and give the problematic plug-in another desultory to duty correctly.

    While this is still far from the much more robust approach employed by Google Chrome, where each tab lives in its own independent process, if Apple's crash statistics are to be believed, isolating plug-ins may generate most of the profit of truly separate processes with a significantly less radical change to the Safari application itself.

    Resolution independence

    When they last left Mac OS X in its seemingly interminable march towards a truly scalable user interface, it was almost ready for prime time. I'm desolate to squawk that resolution independence was obviously not a priority in Snow Leopard, because it hasn't gotten any better, and may relish actually regressed a bit. Here's what TextEdit looks fondness at a 2.0 scale factor in Leopard and Snow Leopard.

    TextEdit at scale factor 2.0 in LeopardTextEdit at scale factor 2.0 in Leopard TextEdit at scale factor 2.0 in Snow LeopardTextEdit at scale factor 2.0 in Snow Leopard

    Yep, it's a bummer. I still remember Apple advising developers to relish their applications ready for resolution independence by 2008. That's one of the few dates that the Jobs-II-era Apple has not been able to hit, and it's getting later every the time. On the other hand, it's not fondness 200-DPI monitors are raining from the sky either. But I'd really fondness to descry Apple accumulate going on this. It will undoubtedly rob a long time for everything to glance and travail correctly, so let's accumulate started.

    Terminal splitters

    The Terminal application in Tiger and earlier versions of Mac OS X allowed each of its windows to be split horizontally into two separate panes. This was invaluable for referencing some earlier text in the scrollback while besides typing commands at the prompt. Sadly, the splitter feature disappeared in Leopard. In Snow Leopard, it's back with a vengeance.

    Arbitrary splitters, baby!Arbitrary splitters, baby!

    (Now if only my favorite text editor would accumulate on board the train to splittersville.)

    Terminal in Snow Leopard besides defaults to the fresh Menlo font. But balky to earlier reports, the One uniform Monospaced Font, Monaco, is most definitely still included in Snow Leopard (see screenshot above) and it works just fine.

    System Preferences shuffle

    The seemingly obligatory rearrangement of preference panes in the System Preferences application accompanying each release of Mac OS X continues in Snow Leopard.

    System Preferences: shuffled yet again Enlarge / System Preferences: shuffled yet again System Preferences (not running) with Dock menuSystem Preferences (not running) with Dock menu

    This time, the "Keyboard & Mouse" preference pane is split into separate "Keyboard" and "Mouse" panes, "International" becomes "Language & Text," and the "Internet & Network" section becomes "Internet & Wireless" and adopts the Bluetooth preference pane.

    Someday in the removed future, perhaps Apple will finally arrive at the "ultimate" arrangement of preference panes and they can every finally paddle more than two years without their muscle remembrance being disrupted.

    Before poignant on, System Preferences has one super trick. You can launch directly into a specific preference pane by right-clicking on System Preferences's Dock icon. This works even when System Preferences is not yet running. kindly of creepy, but useful.

    Core location

    One more gift from the iPhone, Core Location, allows Macs to figure out where in the world they are. The "Date & Time" preference pane offers to set your time zone automatically based on your current location using this newfound ability.

    Set your Mac's time zone automatically based on your current location, thanks to Core Location.Set your Mac's time zone automatically based on your current location, thanks to Core Location. Keyboard magic

    Snow Leopard includes a simple facility for system-wide text auto-correction and expansion, accessible from the "Language & Text" preference pane. It's not quite ready to give a dedicated third-party application a rush for its money, but hey, it's free.

    Global text expansion and auto-correction Enlarge / Global text expansion and auto-correction

    The keyboard shortcuts preference pane has besides been rearranged. Now, instead of a single, long list of system-wide keyboard shortcuts, they're arranged into categories. This reduces clutter, but it besides makes it a bit more difficult to find the shortcut you're interested in.

    Keyboard shortcuts: now with categories Enlarge / Keyboard shortcuts: now with categories The sleeping Mac dilemma

    I don't fondness to leave my Mac Pro turned on 24 hours a day, especially during the summer in my un-air-conditioned house. But I carry out want to relish access to the files on my Mac when I'm elsewhere—at work, on the road, etc. It is feasible to wake a sleeping Mac remotely, but doing so requires being on the same local network.

    My solution has been to leave a smaller, more power-efficient laptop on at every times on the same network as my Mac Pro. To wake my Mac Pro remotely, I ssh into the laptop, then dispatch the magic "wake up" packet to my Mac Pro. (For this to work, the "Wake for Ethernet network administrator access" checkbox must be checked in the "Energy Saver" preference pane in System Preferences.)

    Snow Leopard provides a pass to carry out this without leaving any of my computers running every day. When a Mac running Snow Leopard is save to sleep, it attempts to hand off ownership of its IP address to its router. (This only works with an AirPort Extreme groundwork station from 2007 or later, or a Time Capsule from 2008 or later with the latest (7.4.2) firmware installed.) The router then listens for any attempt to connect to the IP address. When one occurs, it wakes up the original owner, hands back the IP address, and forwards traffic appropriately.

    You can even wake some recent-model Macs over WiFi. Combined with MobileMe's "Back to My Mac" dynamic DNS thingamabob, it means I can leave every my Macs asleep and still relish access to their contents anytime, anywhere.

    Back to my hack

    As has become traditional, this fresh release of Mac OS X makes life a bit harder for developers whose software works by patching the in-memory representation of other running applications or the operating system itself. This includes Input Managers, SIMBL plug-ins, and of course the dreaded "Haxies."

    Input Managers accumulate the worst of it. They've actually been unsupported and non-functional in 64-bit applications since Leopard. That wasn't such a expansive deal when Mac OS X shipped with a whopping two 64-bit applications. But now, with almost every application in Snow Leopard going 64-bit, it's suddenly very significant.

    Thanks to Safari's lack of an officially sanctioned extension mechanism, developers looking to enhance its functionality relish most often resorted to the employ of Input Managers and SIMBL (which is an Input-Manager-based framework). A 64-bit Safari puts a damper on that entire market. Though it is feasible to manually set Safari to launch in 32-bit mode—Get Info on the application in the Finder and click a checkbox—ideally, this is not something developers want to obligate users to do.

    Happily, at least one commonly used Safari enhancement has the noble fortune to be built on top of the officially supported browser plug-in API used by Flash, QuickTime, etc. But that may not be a feasible approach for Safari extensions that enhance functionality in ways not tied directly to the panoply of particular types of content within a webpage.

    Though I pass to rush Safari in its default 64-bit mode, I'll really miss Saft, a Safari extension I employ for session restoration (yes, I know Safari has this feature, but it's activated manually—the horror) and address bar shortcuts (e.g., "w noodles" to glance up "noodles" in Wikipedia). I'm hoping that clever developers will find a pass to overcome this fresh challenge. They always appear to, in the end. (Or Apple could add a proper extension system to Safari, of course. But I'm not holding my breath.)

    As for the Haxies, those usually fracture with each major operating system update as a matter of course. And each time, those determined fellows at Unsanity, against every odds, manage to maintain their software working. I salute them for their effort. I delayed upgrading to Leopard for a long time based solely on the absence of my beloved WindowShade X. I hope I don't relish to wait too long for a Snow-Leopard-compatible version.

    The general trend in Mac OS X is away from any sort of involuntary remembrance space sharing, and towards "external" plug-ins that live in their own, separate processes. Even contextual menu plug-ins in the Finder relish been disabled, replaced by an enhanced, but still less-powerful Services API. Again, I relish faith that developers will adapt. But the waiting is the hardest part.


    It looks fondness we'll every be waiting a while longer for a file system in shining armor to supplant the venerable HFS+ (11 years young!) as the default file system in Mac OS X. Despite rumors, outright declarations, and much actual pre-release code, uphold for the impressive ZFS file system is not present in Snow Leopard.

    That's a shame because Time Machine veritably cries out for some ZFS magic. What's more, Apple seems to agree, as evidenced by a post from an Apple employee to a ZFS mailing list last year. When asked about a ZFS-savvy implementation of Time Machine, the reply was encouraging: "This one is well-known and likely will approach sometime, but not for SL." ("SL" is short for Snow Leopard.)

    There are many reasons why ZFS (or a file system with similar features) is a faultless fit for Time Machine, but the most well-known is its ability to dispatch only the block-level changes during each backup. As Time Machine is currently implemented, if you do a small change to a giant file, the entire giant file is copied to the Time Machine volume during the next backup. This is extremely wasteful and time consuming, especially for great files that are modified constantly during the day (e.g., Entourage's e-mail database). Time Machine running on top of ZFS could transfer just the changed disk blocks (a maximum of 128KB each in ZFS, and usually much smaller).

    ZFS would besides bring vastly increased robustness for data and metadata, a pooled storage model, constant-time snapshots and clones, and a pony. People sometimes inquire of what, exactly, is wrong with HFS+. Aside from its obvious lack of the features just listed, HFS+ is limited in many ways by its dated design, which is based on HFS, a twenty-five year-old file system.

    To give just one example, the centrally located Catalog File, which must be updated for each change to the file system's structure, is a frequent and inevitable source of contention. Modern file systems usually spread their metadata around, both for robustness (multiple copies are often kept in separate locations on the disk) and to allow for better concurrency.

    Practically speaking, deem about those times when you rush Disk Utility on an HFS+ volume and it finds (and hopefully repairs) a bunch of errors. That's bad, okay? That's something that should not occur with a modern, thoroughly checksummed, always-consistent-on-disk file system unless there are hardware problems (and a ZFS storage pool can actually deal with that as well). And yet it happens every the time with HFS+ disks in Mac OS X when various bits of metadata accumulate corrupted or become out of date.

    Apple gets by year after year, tacking fresh features onto HFS+ with duct tape and a prayer, but at a inevitable point there simply has to be a successor—whether it's ZFS, a home-grown Apple file system, or something else entirely. My fingers are crossed for Mac OS X 10.7.

    The future soon

    Creating an operating system is as much a sociable exercise as a technological one. Creating a platform, even more so. every of Snow Leopard's considerable technical achievements are not just designed to profit users; they're besides intended to goad, persuade, and otherwise herd developers in the direction that Apple feels will be most beneficial for the future of the platform.

    For this to work, Snow Leopard has to actually find its pass into the hands of customers. The pricing helps a lot there. But even if Snow Leopard were free, there's still some cost to the consumer—in time, worry, software updates, etc.—when performing a major operating system upgrade. The same goes for developers who must, at the very least, certify that their existing applications rush correctly on the fresh OS.

    The accustomed pass to overcome this kindly of upgrade hesitation has been to pack the OS with fresh features. fresh features sell, and the more copies of the fresh operating system in use, the more motivated developers are to update their applications to not just rush on the fresh OS, but besides rob edge of its fresh abilities.

    A major operating system upgrade with "no fresh features" must play by a different set of rules. Every party involved expects some counterbalance to the lack of fresh features. In Snow Leopard, developers stand to gather the biggest benefits thanks to an impressive set of fresh technologies, many of which cover areas previously unaddressed in Mac OS X. Apple clearly feels that the future of the platform depends on much better utilization of computing resources, and is doing everything it can to do it simple for developers to paddle in this direction.

    Though it's obvious that Snow Leopard includes fewer external features than its predecessor, I'd wager that it has just as many, if not more internal changes than Leopard. This, I fear, means that the initial release of Snow Leopard will likely suffer the typical 10.x.0 bugs. There relish already been reports of fresh bugs introduced to existing APIs in Snow Leopard. This is the exact opposite of Snow Leopard's implied vow to users and developers that it would concentrate on making existing features faster and more robust without introducing fresh functionality and the accompanying fresh bugs.

    On the other side of the coin, I imagine every the teams at Apple that worked on Snow Leopard absolutely reveled in the break to polish their particular subsystems without being burdened by supporting the marketing-driven feature-of-the-month. In any long-lived software product, there needs to be this kindly of release valve every few years, lest the entire code groundwork paddle off into the weeds.

    There's been one other "no fresh features" release of Mac OS X. Mac OS X 10.1, released a mere six months after version 10.0, was handed out for free by Apple at the 2001 Seybold publishing conference and, later, at Apple retail stores. It was besides available from Apple's online store for $19.95 (along with a copy of Mac OS 9.2.1 for employ in the Classic environment). This was a different time for Mac OS X. Versions 10.0 and 10.1 were slow, incomplete, and extremely immature; the transition from classic Mac OS was far from over.

    Judged as a modern incarnation of the 10.1 release, Snow Leopard looks pretty darned good. The pricing is similar, and the benefits—to developers and to users—are greater. So is the risk. But again, that has more to carry out with how horrible Mac OS X 10.0 was. Choosing not to upgrade to 10.1 was unthinkable. Waiting a while to upgrade to Snow Leopard is reasonable if you want to be positive that every the software you faith about is compatible. But don't wait too long, because at $29 for the upgrade, I expect Snow Leopard adoption to be quite rapid. Software that will rush only on Snow Leopard may be here before you know it.

    Should you buy Mac OS X Snow Leopard? If you're already running Leopard, then the acknowledge is a resounding "yes." If you're still running Tiger, well, then it's probably time for a fresh Mac anyway. When you buy one, it'll approach with Snow Leopard.

    As for the future, it's tempting to view Snow Leopard as the "tick" in a fresh Intel-style "tick-tock" release strategy for Mac OS X: radical fresh features in version 10.7 followed by more Snow-Leopard-style refinements in 10.8, and so on, alternating between "feature" and "refinement" releases. Apple has not even hinted that they're considering this type of plan, but I deem there's a lot to recommend it.

    Snow Leopard is a unique and pretty release, unlike any that relish approach before it in both scope and intention. At some point, Mac OS X will surely need to accumulate back on the bullet-point-features bandwagon. But for now, I'm content with Snow Leopard. It's the Mac OS X I know and love, but with more of the things that do it fragile and deviant engineered away.

    Snowy eyes Looking back

    This is the tenth review of a replete Mac OS X release, public beta, or developer preview to rush on Ars, dating back to December 1999 and Mac OS X DP2. If you want to jump into the Wayback Machine and descry how far Apple has approach with Snow Leopard (or just want to bone up on every of the expansive cat monikers), we've gone through the archives and dug up some of their older Mac OS X articles. blissful reading!

  • Five years of Mac OS X, March 24, 2006
  • Mac OS X 10.5 Leopard, October 28, 2007
  • Mac OS X 10.4 Tiger, April 28, 2005
  • Mac OS X 10.3 Panther, November 9, 2003
  • Mac OS X 10.2 Jaguar, September 5, 2002
  • Mac OS X 10.1 (Puma), October 15, 2001
  • Mac OS X 10.0 (Cheetah), April 2, 2001
  • Mac OS X Public Beta, October 3, 2000
  • Mac OS X Q & A, June 20, 2000
  • Mac OS X DP4, May 24, 2000
  • Mac OS X DP3: visitation by Water, February 28, 2000
  • Mac OS X Update: Quartz & Aqua, January 17, 2000
  • Mac OS X DP2, December 14, 1999

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    PEOPLECERT [4 Certification Exam(s) ]
    PMI [15 Certification Exam(s) ]
    Polycom [2 Certification Exam(s) ]
    PostgreSQL-CE [1 Certification Exam(s) ]
    Prince2 [6 Certification Exam(s) ]
    PRMIA [1 Certification Exam(s) ]
    PsychCorp [1 Certification Exam(s) ]
    PTCB [2 Certification Exam(s) ]
    QAI [1 Certification Exam(s) ]
    QlikView [1 Certification Exam(s) ]
    Quality-Assurance [7 Certification Exam(s) ]
    RACC [1 Certification Exam(s) ]
    Real-Estate [1 Certification Exam(s) ]
    RedHat [8 Certification Exam(s) ]
    RES [5 Certification Exam(s) ]
    Riverbed [8 Certification Exam(s) ]
    RSA [15 Certification Exam(s) ]
    Sair [8 Certification Exam(s) ]
    Salesforce [5 Certification Exam(s) ]
    SANS [1 Certification Exam(s) ]
    SAP [98 Certification Exam(s) ]
    SASInstitute [15 Certification Exam(s) ]
    SAT [1 Certification Exam(s) ]
    SCO [10 Certification Exam(s) ]
    SCP [6 Certification Exam(s) ]
    SDI [3 Certification Exam(s) ]
    See-Beyond [1 Certification Exam(s) ]
    Siemens [1 Certification Exam(s) ]
    Snia [7 Certification Exam(s) ]
    SOA [15 Certification Exam(s) ]
    Social-Work-Board [4 Certification Exam(s) ]
    SpringSource [1 Certification Exam(s) ]
    SUN [63 Certification Exam(s) ]
    SUSE [1 Certification Exam(s) ]
    Sybase [17 Certification Exam(s) ]
    Symantec [134 Certification Exam(s) ]
    Teacher-Certification [4 Certification Exam(s) ]
    The-Open-Group [8 Certification Exam(s) ]
    TIA [3 Certification Exam(s) ]
    Tibco [18 Certification Exam(s) ]
    Trainers [3 Certification Exam(s) ]
    Trend [1 Certification Exam(s) ]
    TruSecure [1 Certification Exam(s) ]
    USMLE [1 Certification Exam(s) ]
    VCE [6 Certification Exam(s) ]
    Veeam [2 Certification Exam(s) ]
    Veritas [33 Certification Exam(s) ]
    Vmware [58 Certification Exam(s) ]
    Wonderlic [2 Certification Exam(s) ]
    Worldatwork [2 Certification Exam(s) ]
    XML-Master [3 Certification Exam(s) ]
    Zend [6 Certification Exam(s) ]

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