On Aug 24, 2005, at 2:14 PM, Sam Phillips wrote:
Do you have the urge to allocate >4GB of a memory to a process?
If not,
most of the reason for using a 64bit OS are gone. In fact, running a
32bit OS on a 64bit amd64 processor is probably going to be slightly
faster than a 64bit OS for many things.
I would think (and I'm most likely wrong) that if you had >4GB of
memory
you wouldn't be able to address it for even 4k of allocation in 32 bit
mode.
The theoretical maximum amount of memory you can address *per
process* on a Pentium Pro or better CPU is 4GB, or 2^32. It is
actually much less than this because of I/O ranges, memory reserved
for the kernel, and the overall inferior design of x86. The maximum
amount of memory you can have in a x86 machine is 2^36 or 2^42,
depending on which model of Intel CPU you have purchased. Note the
difference between per process and total available memory.
This restriction totally goes away with the new 64-bit extended x86
CPUs, though a 32-bit app running on a 64-bit CPU on a 64-bit OS
still has the restrictions outlined above.
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