All That Jazz: 32 and 64-bit Macs, EFIs, Kernels & Apps

| Snow Leopard

All Intel-based Macs can run Snow Leopard, and that's the most important take-away here. However, not all Macs can boot Snow Leopard into the 64-bit kernel, and a few older Intel Macs can't even run 64-bit software. Here are some notes to help you make sense of it all.

For reference, here are the system requirements for Snow Leopard.

The first thing to remember is that a Mac has to have a 64-bit CPU to run 64-bit apps. The Core 2 Duo, (Merom and Penryn) and the Xeons are 64-bit CPUs. However, the original MacBook Pro and Mac Minis with a Core Duo had 32-bit CPUs. So they can't run modern 64-bit applications, and everything runs as 32-bits. Snow Leopard is smart about how to do that.

The next thing to know is that even if a Mac is fairly modern, and has a 64-bit CPU, only the latest ones can boot into a 64-bit kernel. (Abbreviated as "K64" by Apple in the chart below.)  They need what's called a 64-bit EFI (Extensible Firmware Interface) to do that, a decision Apple enforced for compatibility. Here's a list, supplied by Apple, that shows which Macs can boot into a 64-bit kernel. These are all fairly recent Macs.


K64 Macs

Macs that can boot into 64-bit kernel

The final thing to note is that even if a Mac with a Core 2 Duo or Xeon is not on the list above and has a 32-bit EFI and can only launch a 32-bit kernel (for now), it can still run 64-bit apps. Apple planned ahead for that as a long sequence of building towards a 64-bit system, yet maintaining backwards compatibility.

Even so, we're not quite there yet in terms of 100 percent 64-bit systems. As mentioned on Monday, not every kernel extension has been converted to 64-bits, so Apple has had to take things one step at a time. That's why the Snow Leopard kernel boots into 32-bit mode by default on every Mac but the Xserve. To make sure everything "just works."

So what's the bottom line? So long as you have a Core 2 Duo or Xeon CPU, you'll be able to run 64-bit apps and address more than 2 GB of RAM. Just how much physical RAM you can address is still limited*, but a 64-bit virtual address space is a whole lot larger than your hard disk, so you're in good shape for now.

Eventually, all kernel extensions will be 64-bit and the Macs on the list above (or later) will eventually boot into 64-bit mode by default.** But for now, it's no big deal that you may not have the latest and greatest Mac, on the list above, that is "K64" compatible. You still have a healthy address space, access to lots of RAM, a 64-bit Finder and many 64-bit applications by Apple -- with more to come from developers.

So it's really just a technical nit. You can breathe easy.

There's a handy app that can tell you all about your 32 or 64-bit capabilities, your EFI, and what mode the Mac's booted into. But follow the warning when it launches!


Starup Mode selector

Startup Mode Selector


* I'll talk about the address bus size in a future article.

** Whether Apple will offer EFI updates from 32 to 64 bits for some Macs is not known.

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So I won’t be able to boot my Late 2008 Macbook into 64 bit.



So I won?t be able to boot my Late 2008 Macbook into 64 bit.

No, but you can still run 64-bit applications on it.


Oh yeah I know, and it isn’t like I have any 64 bit apps (except for some of the Apple Apps I believe). It’s just, I don’t know, a status thing maybe. Digital snobbery. One-upsmanship.

For what I do with my MacBook, I don’t think it’ll make a tinkers-damn worth of difference .


John, I have a March 2009 Mac mini. It has a 64-bit Core 2 Duo CPU and a 64-bit EFI yet Apple somehow prevents it from booting the 64 bit kernel. Any chance you could find out how that is prevented and, more importantly, why?

As far as I can see, this Mac mini should be “capable” too…

Derek Williams

I installed Snow Leopard on my 2007 Intel Mac (twin dual core = ‘quad core’) and it slowed the machine down incredibly, taking up to 10 minutes to go to incomplete boot, had to start in safe mode, Audio/MIDI Setup app hung etc etc.  It was a complete disaster from start to finish.  So I used the trusty Time Machine to back up to 10.5.8 and all is well again. Goodbye Snow Leopard, it’d be great to say “it was nice knowing you”, but it really wasn’t.


John, I have a March 2009 Mac mini. It has a 64-bit Core 2 Duo CPU and a 64-bit EFI yet Apple somehow prevents it from booting the 64 bit kernel. Any chance you could find out how that is prevented and, more importantly, why?

You have very very little advantage from a 64 bit kernel. The 64 bit kernel is important for people with tons of memory (like more than 64 GB), you don’t fall into that category. And a 64 bit kernel requires 64 bit drivers, which are not available for each and every hardware. So 64 bit kernel for a Mac Mini would be very very little gain, and possibly a lot of trouble because some hardware isn’t working. I think the Intel integrated graphics doesn’t have 64 bit drivers; if you MacMini has that, you would really miss the driver, because you wouldn’t be able to see anything.

All the 64-bit applications will run just fine in 64 bit; they don’t care what the kernel is.



Is it possible that you were a bit impatient? I had upgraded my old 2007 MacBook (white) and experienced similar problems (initially). The installation itself took over an hour. Upon completion, rebooting took some 15 minutes (at least). When it finished, I restarted, and it took a long, long time again to re-boot. When I logged into other user profiles, it took (seemingly) forever for each profile to log in on the first try.

However, after having logged into every profile at least once, and having re-booted the Mac twice, it now starts up in 35 seconds, shuts down in 15 seconds, and is so incredibly faster that I can simply not believe it. For me, Snow Leopard was by far the most effective upgrade between Mac versions (and I’ve been doing them since System 7.1)

Derek Williams

Vasic - thanks for your helpful comments.

There were a couple of other things my post didn’t mention:
? when the login screen first appeared on restart after installation, and after the delay you mentioned already, the USB QWERTY keyboard was not detected so I couldn’t type my password, although the mouse moved the cursor ok, also my 2nd 30” monitor was not detected and appeared totally black; I had to hold down the computer’s power key to force it to shut down and restart
? when I got to the Finder on a reboot, the Audio/MIDI Setup application hung and never progressed to seeing any devices, however reboot in Safe mode did allow it to launch and see the devices greyed out as well as displaying both the monitors and instantiating the USB QWERTY keyboard
? ebooting once again after the safe mode boot caused the computer to appear to hang on two pale blue monitors, and so I decided enough was enough; maybe this was the bit where I was impatient and should have waited another quarter of an hour

To my mind, having a newly installed operating system hang the machine forcing a hard restart, disable the USB QWERTY keyboard, hang the Apple AUDI/MIDI utility application on first launch was so horrendous I thought “Snow Leopard is not for me, nor for this computer” and raced to the Time Machine as fast as my digits could carry me.

I have raised a support ticket with Apple and they have kindly given me my very own Tech Support guy, but as I am dismantling my studio this very afternoon, will have to delay installation of Snowie until I return in a new premises at the end of October, by which time they may have a version that works for me. Although impatience may perhaps have had something to do with some of the above steps, I don’t think the logon screen should have hung nor the 2nd monitor blacked out, nor the Audio/MIDI Setup utility hung, so I think it may also have something to do with the fact that although it is an Intel Xeon Quad Core (= 2x Dual Core), my machine only has an EFI32.


HOLD 6 and 4 keys on boot… boots to 64 bit if computer is capable

I did a back up via Super Duper prior to install. Permissions fixed
Then dropped in the SnowJob disk… went to the TV and an hour later came back and all was done. No problems on a 2.4 MBP 4 gigs. I think some people leave things plugged in. like a USB or Ethernet cable. Just go virgin, disconnect everything, fix permissions and back up
If you complain that this OS is buggy… I think perhaps it is like pointing a finger of blame.. then look at that fist.. four fingers pointing back. Hmmmm



My two Macs were MB and MBP, with no external hardware and no unusual software. In all fairness to you, it looks like your setup is much more than just the computer, keyboard, mouse and monitor. Judging by the fact that your Audio/MIDI utility froze, I’m assuming you have some audio (or MIDI, or both) hardware (Digidesign? M-Audio?), for which the current drivers won’t work with SL. Digidesign is notorious for taking their time to update their drivers and utilities to work with Apple’s latest OS (and Snow Leopard has been in Beta for the longest time; they had plenty of time to prepare). You’re smart for using Time machine.

I’m sure your problem will eventually be resolved. It would be a shame to have to wait too long, since SL is one fast, fast, fast OS.


I think the Intel integrated graphics doesn?t have 64 bit drivers

That is incorrect. The 2009 Mac mini is equipped with Nvidia 9400M graphics are operates in full 64-bit mode.

John Martellaro

If the computer isn’t on the list above, but has a 64-bit EFI, then my guess is that Apple is blocking the boot into 64-bit kernel for technical reasons. As for a remedy ... at your own risk ... I read about the etkas’ pcefiv10.1 bootloader.


Let me try that in English this time (why aren’t posts editable?):

The 2009 Mac mini is equipped with Nvidia 9400M graphics for which Snow Leopard most definitely includes 64-bit driver software. In fact, the 9400M is also fully compatible with the new OpenCL technology and all Mac OS X graphics acceleration technologies too.

As far as I can tell, Apple doesn’t have a reason to prevent the 2009 Mac mini from booting a 64-bit kernel. It may, however, have an excuse. I’m just wondering what that might be…


Thanks, John (and thanks for the tip!).

I’d love to know what Apple’s “technical reasons” might be…


Try booting with the 6 and 4 key pressed
No need for more hackware.. and what good will 64 do for you.. or the whinPC
crowd other than saying we boot 64? Amazing this forum allows such juvenile discussions or rat holes…
Time to move on or go back to Leopard and ask for a refund. I like Sl and see an improvement in areas that needed tweaking. It should have been a regular update though.. I did need a new boot disk however.. so I am happy for that

And this disk is not machine specific as so many OE disks ship. Use it on any Intel Mac in your arsenal. $25 is cheap for that alone.


I like Sl and see an improvement in areas that needed tweaking. It should have been a regular update though

That’s a childish attitude, Tom. Do you always expect to get something for nothing?


I was simply quoting another, Leo Laporte. I agree with him on many portions of this upgrade. However, I did pay. I also pay for all my software. Having an opinion is not childish but you make my point of the whining. Look how the next guy high jacks the thread. Amazing.
As for getting nothing .. I have bought over 20 macs. First was a simple SE running OS 6. So deasys, speaking candidly you speakith too much. Making allegations on an opinion.. do you work for the government, say the Green Committee?


As far as whether this should have been a free update or not, let’s remember that for 10.5 users i10.6 was $29, and $9 for recent Mac Purchasers. So while I can see both sides of the argument (It’s a major code change v. I don’t see any huge improvement) IMO Apple split the difference rather well. Most full number upgrades are something like $129.


After a few days.. I must say this is a greater improvement than even Apple let on. It comes out slowly. Most of the better aspects will surely become evident on next generation of Macs


I bought an early 3GHz Quad-Core Intel Xeon MacPro for doing data crunching and modeling and assumed that it was ready to run as a 64-bit some day when we got to that advancement.

However, today I discover that Apple took a 64-bit processor and hampered it with a Boot ROM Version that limits it to 32-bit.
I feel like a dope and more to the point I feel powerless because now I have to pry that Apple release firmware that updates the RBV EFI to 64-bit when programs start becoming availible for the new memory allocation limits.
Does anyone one know if there is any chance Apple will deal with the EFI issue on a lot high end MacPro’s (because there was reason to do this) in the future.
If they don’t they might be losing a loyal customer.

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