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.