Just received my copy of Mac OS X 10.6 Snow Leopard!
One of the main new features of this version is its 64-bit kernel. However, there are a couple of catches: First, even if you have a shiny Intel Core 2 Duo Mac you must have a 64-bit EFI in order to boot the 64-bit kernel.
ioreg -l -p IODeviceTree | grep firmware-abi
If you get EFI64 you’re in luck, otherwise tough… I got lucky: I do have a 64-bit EFI. Nice.
Second, even then all Macs (except Xserve) boot the 32-bit kernel by default. To use the 64-bit kernel you can either press ‘6′ and ‘4′ everytime you boot your Mac, or you can edit
com.apple.Boot.plist as follows:
2. Find the string:
3. Change it to:
That’s it, you’re set. (if you ever need to boot in 32-bit mode, just press ‘3′ and ‘2′ during boot).
Update (31st August):
After having made the modification above, I wanted to insure that the kernel used was indeed the 64-bit one. To do that:
Which for me unfortunately gives:
Darwin Kernel Version 10.0.0: Fri Jul 31 22:47:34 PDT 2009; root:xnu-1456.1.25~1/RELEASE_I386 i386
So beware: a 64-bit EFI is not a guarantee that you’ll be able to use the 64-bit kernel. Especially, apparently iMac 7,1 (my case) cannot use the 64-bit kernel in any case.