Messages in this thread | | | Date | Mon, 3 Jan 2005 14:15:16 -0800 | From | William Lee Irwin III <> | Subject | Re: Max CPUs on x86_64 under 2.6.x |
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On Mon, Jan 03, 2005 at 10:00:41PM +0800, Colin Coe wrote: > Why is the number of CPUs on the x86_64 architecture only 8 but under i386 > it is 255? > I've searched the list archives and Google but can't find an answer.
i386 machines have had interrupt controllers and "large scale" systems (to the extent that 32-bit machines can be so) developed for some time. x86-64 machines are newer, and it is the maintainer's preference to start with a fresh codebase for the APIC.
So what you see is not a reflection of x86-64's capabilities, but rather, of the newness of the architecture and the codebase's desire to be "legacy-free" in manners that don't pose the threat of causing immediate problems.
It is not now limiting the capabilities of x86-64 machines because x86-64 machines of 64 cpus or larger have yet to be produced. For the record, I'm unaware of SSI i386 machines larger than 64 processors. 255 represents nothing more than a theoretical limit of hardware capabilities, and no i386 machine larger than 64 processors has ever been constructed to the best of my knowledge.
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