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32-bit Kernel Core 2 Duo Macs Can Run 64-bit OS X

Simon Royal - 2012.04.03

I recently wrote about some Core 2 Duo Macs not being able to boot to a 64-bit kernel (see More Macs Left Behind by Developer Preview 2 of OS X 10.8 Mountain Lion), and since then I have done some further research.

After my article was published, I was contacted by a fellow reader who has the same Mac as I do (an Early 2009 MacBook). He is running OS X 10.7 Lion on his and running it in 64-bit kernel mode.

It has the same Mac identifier model, boot ROM version, and SMC version as mine, and as far as I can tell is genuine. I checked both our serial numbers on the PowerBook Medic Serial Checker, and both show up as identical Macs.

Early 2009 MacBook running OS X 10.6

When booting OS X 10.6 Snow Leopard, the Early 2009 MacBook boots with a 32-bit kernel.

Early 2009 MacBook running OS X 10.6 with 32-bit kernel

Early 2009 MacBook running OS X 10.6 with 32-bit kernel.

It would appear that some of those Macs that cannot boot to a 64-bit kernel in Snow Leopard can boot to a 64-bit kernel in Lion. This seems not to be a hardware limitation and was a deliberate decision by Apple, but why?

When Apple launched Snow Leopard in 2009, it was touted as a 64-bit OS, which it is. However, it would appear that there were either no available drivers or kernel extensions for some of the hardware components or they were not stable enough in 64-bit mode.

This seems to be the reason some Macs will only boot to 32-bit kernel. Some Macs boot by default to 32-bit kernel but can be made to boot to 64-bit kernel. This seems rather sloppy on Apple’s part. Okay, so they can be forgiven for not including it on launch, but subsequent updates could have rectified this.

This is good news for the likes of me. I have yet to verify it personally, but I have seen screen shots confirming my Mac running a 64-bit kernel in Lion.

Early 2009 MacBook running OS X 10.7

When booting OS X 10.7 Lion, the same MacBook boots with a 64-bit kernel.

Early 2009 MacBook running OS X 10.7 with 64-bit kernel

With this being one of the requirements of the Developer Preview 2 of Mountain Lion, it has put me a little more at ease that my Mac should be able to run it.

At some point I shall install Lion on my MacBook – probably on an external drive to begin with, so as not to interfere with my current Snow Leopard setup. Then I will be able to see firsthand.

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