cK-Gunslinger wrote:

That's *exactly* what I just said. *If* the code has been recompiled to
take advantage of the new 64-bit features, it will perform better;
otherwise, not.

A 64-bit CPU gives you the ability to use 64-bit memory address,
allowing you to have a *lot* more addressable memory that 32-bit (which
are 'limited' to ~4GB). Also, the registers are 64-bit, allowing you do
perform 64-bit calculations in a single step, as opposed to doing them
twice with 2 32-bit numbers. That's it. That's all that's required for
a CPU to be '64-bit'. If your applications use a lot of 64-bit
number/integers (most do not), then you might see some speedup,
Otherwise, not. Simple.

64-bit = 'more memory, larger native numbers'
64-bit != 'inherently faster performance'

But like I said before, all the new 64-bit CPUs include numerous other
architectural enhancements that will outperform current 32-bit CPUs, so
your apps *will probably* perform better on an Opteron than your current
p4, but *not* because the Opteron is 64-bit, but rather in spite of it.

That's a nice opinion, now, do you have any examples using real-world
processors and real-world code to support it?

What you claim to be saying and what you are actually saying seem to be more
than a little at variance. If the advantages you cite are the only ones
that a 64-bit processor provides then why does 64-bit Linux run so much
faster than 32-bit Linux on the same hardware?

J. Clarke wrote:
cK-Gunslinger wrote:


All things being equal, a 64-bit machine (CPU + OS) will typically be
*slower* than a 32-bit machine. Now, all things are *never* equal and
the current line-up of 64-bit CPUs (AMD64, Opteron, etc) have many
hardware enhancements (extra registers, larger caches, faster memory
interconnects, etc) that will increase overall performance.

That being said, if you own a 64-bit CPU and are running in 32-bit mode,
will you get better performance simply by installing WindowsXP-64 and
some 64-bit drivers? Possibly, but only if the OS/drivers have been
tweaked to take advantage of the CPU/chipset's new features. The
general "64-bit-ness" of the software does not make anything faster over
32-bit.


I'd be interested in knowing on what you base this conclusion.

FWIW, with the Opterons Linux shows a marked performance improvement when
recompiled as 64-bit code.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)