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MacPro/new iMac are the first systems with 64-bit kernel
Authored by: rorya on Oct 01, '06 08:57:39PM

One of the advantages of the IBM PowerPC 970 (used in the G5s and iMac G5) is that it switch between executing 32-bit and 64-bit executables, on the fly. This capability made it very simple for Apple to support 64-bit applications, as xnu (the kernel) only needed minor changes, and more importantly, xnu and all the kexts could remain 32-bit. So the barrier to entry was quite low, to support 64-bit

However, on EM64-T/AMD64 (PCs) this is not possible, where you can only choose the mode you want at bootup, that is, 32-bit or 64-bit modes. It cannot switch on the fly, like the PewerPC 970 can. So, this limitation has forced Apple to change xnu and all the kexts to be 64-bit, for the first time, on these new 64-bit Intel Core 2 systems. If the xnu (the kernel) runs in 64-bit mode, it can then run 64-bit applications and emulate 32-bit. However, when it comes to the kernel space (ring 0), it and its extensions must be 64-bit. So as others have mentioned, it's quite likely that the reason xnu is crashing on boot is due to installing a 32-bit kext, which of course, won't work.

This is one of the advantages PowerPC has over IA/AMD64.

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"Any sufficiently advanced technology is indistinguishable from magic" - Arthur C. Clarke



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