[Cialug] Opteron and 64 bit architecture question

[Nathan C. Smith]

I have been paying a good deal of attention to the AMD 64 architecture
lately.  A trade rag recently said that the Pentium solution to accessing
more than 4 gigs of RAM was kind of a kludge involving virtualization of
addresses.  The explanation sounded plausible.  The New 64-bit
architectures, having a longer word and address length will not experience
this problem.

My question is, if you run a 32 bit program on a 64 bit machine
(particularly AMD), does it have to recreate this memory access kludge in
the "emulation mode", or is this one of the ways it can give a little boost
to a 32 bit system running on a 64 bit architecture.

If I buy 64 bit machines now, and run 32 bit Oss on them, I will be
future-proofed to some degree, but will I get any benefit for the 32 bit OS
today?

Anyone with an Opteron happy with it in 64 or 32 bit "mode"?  I have an
Athlon 64 Machine at work running Fedora Core 3 64.  It is a fast machine,
but I can't say that is is significantly faster than other machines,
subjectively, it actually "felt" faster running 32 bit FC3.

I'd like to hear some more insight.

-Nate