On Thursday 21 May 2009, Joshua Baker-LePain wrote: > On Thu, 21 May 2009 at 4:59pm, Robert Heller wrote > > > No, you are not wrong. All x86 flavered 64-bit processors will run as > > 32-bit (i686) processors and when running in 32-bit mode are > > effectively just a i686 as far as any 32-bit program can tell. There > > is no reason NOT to just install a straight 32-bit OS on such a machine > > if there is less than 4gig of virtual memory and non-of the programms > > being run has any reason to use the 64-bit address space. Web hosting > > That's not strictly true. On some x86_64 chips, there are extra registers > which are only available when running in 64-bit mode. Running without > those registers can hamper performance, even if the program isn't using > the larger address space. There's a 2nd factor. On 32-bit you loose full flexibility memory wise when you pass 920-ish MB. After that you're split up into low-mem and high-mem. On 64-bit, of course, all memory is low-mem. /Peter > This can make a big difference, e.g., in the > HPC space. Web hosting, yeah, probably not so much. But just saying > "64bit iff >4GB RAM" doesn't tell the whole story.
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