32-bit vs. 64-bit x86 Speed

I recently made a claim on the Beowulf email list that somebody
questioned me on. After some reflection, I'm not as sure as I once was
that I'm correct. I'm wondering what you compiler people have to say
about this.

Here's what I said:

"One thing I've noticed about 64-bit computing in general is that it's
being oversold. The **only** reason for running in 64-bit mode is if
you need the additional address space. Indeed, for some apps this is
critical and 64-bit computing solves a real problem. For apps that
don't need the extra address space, the benefits of the additional
registers in x86-64 are nearly undone by the need to move more bits
around, so 32-bit and 64-bit modes are pretty much a push. When you
add the additional difficulty of getting 64-bit drivers and what-not,
I don't think it's worth messing with 64-bit computing for apps that
don't need the address space."

Let's say you're a Linux user who never needs to run programs that
don't fit in 32-bits. Would you run a 32-bit or a 64-bit version of
Linux? You compiler people probably have intimate knowledge of the ISA
issues here so I'm interested in what you have to say.

Cordially,
--
Jon Forrest
Unix Computing Support
College of Chemistry
173 Tan Hall
University of California Berkeley
Berkeley, CA
94720-1460
510-643-1032
jlforrest@xxxxxxxxxxxx

.

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