Lion is the first OS X release to drop support for any Intel processors – machines using 32-bit Core Solo and Core Duo machines (sold mostly in 2006 at the very beginning of the Intel switch) aren’t able to install the new OS without hacking (which is outside the scope of this review). This is common practice for Apple, whom habitually irks a small but vocal portion of its userbase who insist (not altogether unreasonably) that their Macs are still running just fine.

Apple usually doesn’t do this lightly – in most cases, dropping support for older models is done to move the platform forward (though, as when 10.4 dropped support for Macs without FireWire, it can also be done to push particular proprietary technology). Just as Snow Leopard pulled support for PowerPC Macs to emphasize Intel development, Lion will pull support for x86 to push 64-bit development.

I’ve seen quite a bit of confusion on this topic (and there was quite a bit when Snow Leopard trumpeted full 64-bit support at its release), so I want to go into some detail about the history of 64-bit OS X. If you’re not interested in that, though, let me lay out the most important stuff in brief:

  • Core Solo and Core Duo-equipped Macs are the only Intel Macs being dropped by Lion. Even if it can’t boot the 64-bit kernel of Lion or support 64-bit EFI, any Mac that came with a Core 2 Duo (or any 64-bit capable Intel processor) can install and run Lion without modification.
  • Core 2 Duo-equipped Macs that don’t support OS X’s 64-bit kernel or 64-bit EFI can still run 64-bit apps, which can address more than 4GB of RAM.
  • The Lion installer isn’t actually doing checks for processor capability, but for your Mac’s model identifier, meaning that Core Solo and Core Duo Mac Minis and iMacs that were later upgraded to Core 2 Duo processors will still fail to install Lion without modification because the installer assumes they’ll be running 32-bit processors (though if you can get Lion running, your processor should be able to run everything just fine). Remember that these processor upgrades, while technically possible, were never supported by Apple.

Now for a history lesson, combined with about as much information about Lion’s 64-bit support as you could ever want.

64-bit in Mac OS X 

OS X’s 64-bit implementation differs significantly from that of Windows, which treats its 32-bit and 64-bit versions as two distinct operating systems stored on different install media. This is done mostly to maintain Windows’ compatibility with older applications – moving or renaming things like the System32 folder would break programs that expected it to be there – and as a result the two are separated to the point that there isn’t even an upgrade path between 32-bit Windows and 64-bit Windows. Because of this, and because Windows applications and drivers usually have distinct 32-bit and 64-bit versions, Windows’ transition to 64-bit has been slightly rockier and slightly more visible to the user.

OS X, on the other hand, has made a more gradual transition between 32-bit and 64-bit, with support added slowly over the course of multiple releases. OS X 10.3 and 10.4 came with some basic support for 64-bit underpinnings, but support for 64-bit applications didn’t come until 10.5 Leopard (which included the 64-bit version of Cocoa, OS X’s primary API). The same technology that allowed developers to offer Intel and PowerPC programs as a single Universal Binary also allows developers to release single packages that support both the x86 and x64 architectures.

While Leopard brought support for 64-bit apps that can address more than 4GB of memory, Snow Leopard actually introduced an OS kernel (along with 64-bit kernel extensions and drivers) that was 64-bit, though a 32-bit kernel was used by default on almost all Macs whether they supported the 64-bit kernel or not. This was done mostly to give software developers time to get 64-bit KEXTs and drivers ready – since Snow Leopard’s release, Apple has released both Mac Pros and MacBook Pros that boot with the 64-bit kernel by default (and OS X Server uses a 64-bit kernel by default in even more models, as outlined in this Apple support document).

Lion pushes this a bit further by booting a 64-bit kernel on basically any Mac that supports it – the 2007 aluminum iMac, the 2009 unibody MacBook Pro, and the 2010 MacBook Air I used booted Snow Leopard with the 32-bit kernel by default, but booted with the 64-bit kernel for Lion (and the iMac and the Air didn't even support the 64-bit kernel in Snow Leopard). That being said, Lion still includes the 32-bit OS X kernel, and will use it on machines that don’t support the 64-bit kernel – you can still make full use of 64-bit apps and more than 4GB of RAM, even though the OS kernel itself can’t. This won't usually be a big deal, since the Macs that can’t use the 64-bit kernel are mostly older models with RAM caps at or under 4GB anyway.

In both Snow Leopard and Lion, you can check your kernel's 64-bitness by opening up System Profiler/Information, going to the Software section, and looking at the "64-bit Kernel and Extensions" field. Yes means a 64-bit kernel, No means 32-bit.

Lion with a 32-bit kernel on a 2008 MacBook

Support for the 64-bit kernel requires four things to be true: You need (obviously) a 64-bit Intel processor, a Mac that supports 64-bit EFI, hardware for which OS X has 64-bit drivers (graphics cards are usually the problematic area here), and a Mac that has not been specifically disallowed from booting the 64-bit kernel – most new Macs support the 64-bit kernel, but white MacBooks are still artificially limited by Apple from booting the 64-bit kernel in Snow Leopard despite hardware that fully supports it. Most if not all of these artificial limitations have been removed in Lion for machines that meet the other 64-bit criteria.

Apple began really pushing 64-bit with its marketing for Snow Leopard, and has been dropping support for 32-bit APIs like Carbon for years – giving developers aiming for Lion guaranteed 64-bit capability both enables them to better take advantage of the architecture improvements and saves them the effort (and file size) of also supporting a 32-bit version. That said, 32-bit programs will continue to run fine in Lion, just as they ran fine in Snow Leopard and Leopard before it.

The hidden downside of the 64-bit push for Core Solo and Core Duo users is that, as developers slowly move to 64-bit only applications, we’ll start getting more and more things that won’t run on 32-bit Snow Leopard despite being supported on 64-bit Snow Leopard (the same thing is currently happening to Leopard users still using PowerPC processors – Flash Player, Google Chrome, Firefox 4, and Microsoft Office 2011 are all fairly mainstream apps that run in Leopard but only on Intel machines). The disappearance of 32-bit programs will be gradual, but it is something to be wary of if you continue to use a Core Solo or Core Duo Mac going forward.

What gets dropped next?

This discussion isn’t complete without a look into our murky crystal ball to see what Macs will be dropped by the next version of Mac OS. The continued push for 64-bit makes me think that we could see machines incapable of running the 64-bit kernel dropped, though that line in the sand could be too faint for most consumers to see, especially given the scarce and not-always-clear documentation on what Macs support it in the first place.

It’s worth noting that Apple could easily issue EFI, KEXT, and driver updates for any Macs it wants to enable to run the 64-bit kernel – there are some models like the 2007 aluminum iMac (iMac 7,1, for those who prefer information pulled from System Profiler) that didn’t support Snow Leopard’s 64-bit kernel, but boot with Lion’s 64-bit kernel by default.

The more likely cutoff point for 10.8 (or OS XI, or whatever comes next) is graphics-related – Apple has been shipping mostly OpenCL-capable products since 2009, and by the time the next Mac OS is upon us (2013-ish, at the current rate), products pre-dating OpenCL support will mostly be four and five years old (roughly the same age as the current Core Solo/Duo Macs). If Apple continues its trend of dropping products that hold back the platform in one way or another, pre-OpenCL machines seem to be the most likely candidates on the chopping block.

Screen Sharing, Boot Camp, Migration Assistant SMB File Sharing in Lion
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  • VMFnet - Friday, July 22, 2011 - link

    I just installed Lion on a OCZ Vertex2 SSD and it still doesn't support TRIM. I guess support for this feature is limited to stock Apple SSDs only. Reply
  • Sapan - Friday, July 22, 2011 - link

    Thanks for the reply. It is a shame that there still is no TRIM support.

    In the mean time I would recommend checking out a 3rd party program called TRIM Enabler:
    http://www.groths.org/?page_id=322

    Though the program is designed for Snow Leopard it works for Lion, but they are making a new version for Lion.
    Reply
  • mdlam - Friday, July 22, 2011 - link

    I love how these diehard Apple fans are trying to resolve their discomforting feelings of exorbitant expenditure to Apple by

    A: Unreasonably denigrating other competitive alternatives.
    B: Exaggerating the usefulness of certain proprietary tools.
    C: Empathizing with the company's goals/missions/values

    All to resolve the realization that they are paying more money than what they are getting, which is...

    A totally outdated OS made to look streamline
    A pretty cool looking computer that uses tunnel fans (which are extremely loud) and likes to overheat.
    I used Snow Leopard on my Mac Mini for about 2 months and hated it. I think people force themselves to like OSX just because their laptop looks cool.
    Horrible graphics speeds. Their BEST video card that you can fit into a their $4500 Mac Pro, is a ATI 6500 series, which is like a 100 dollar card, and offers pathetic performance for gaming--I had a 6950 2gb and that was barely enough. You can argue that Mac pro's should be used for graphics design and other things and not gaming. If that's the case I don't see why they don't put a FireGL or other designer cards in. In any case, who buys a $4500 computer that comes with a bullcrap video card? Some people are IDIOTS.
    Reply
  • mdlam - Friday, July 22, 2011 - link

    Edit: A $170 dollar video card, 6870 1gb...Which is a complete piece of garbage card that is 30% slower than the 5970 1gb. Guess how much the upgrade is? $200.

    Post is based off of cognitive dissonance theory
    Reply
  • parlour - Monday, July 25, 2011 - link

    Macs don’t seem to be the right choice for you. That’s alright. Just don’t claim that everyone else has the same needs as you. Reply
  • sjinsjca - Saturday, July 23, 2011 - link

    The test with the SSD is intriguing but there's a possibility that the FileVault performance hit might be less in the case of a conventional hard disk.

    Reason: hard disks are slower than SSDs, so there would be more idle states in which the OS could be performing encryption/decryption tasks.

    Worth a spot-check.
    Reply
  • EnerJi - Sunday, July 24, 2011 - link

    That's a great point. I'd also love to know if the performance impact decreases with an HDD. Reply
  • johnmacward - Tuesday, July 26, 2011 - link

    What annoys me is the fact that the recovery partition doesn't keep a copy of the Lion installer for instant re-installation - and with a bit of Apple magic even a copy that updates as the OS updates.

    A download each time is a possibly expensive prospect considering we all have data caps of some kind.

    It also turns a reinstall into a shockingly long 4 hour job which is a major pain.
    Reply
  • luca108 - Tuesday, July 26, 2011 - link

    Small detail, but in the review you said you could only launch Launchpad by clicking the dock icon or using spotlight, but you can also set it as a hot corner. This is what I personally do... top left corner set for Launchpad and I can quickly get in and out of it to find my apps and utilities.

    I'm not suggesting it's quicker than using an apps stack on the dock... actually, its the exact same. But it definitely is faster than clicking the Launchpad dock icon or using spotlight to launch it.
    Reply
  • Thrakazog - Tuesday, July 26, 2011 - link

    Does anyone know if Lion extended trim support to 3rd party SSD's, instead of only the ones apple provides ? Reply

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