Enquiry,,,

[Jonathan Berry]

On 2/2/07, Dmitriy Kropivnitskiy <nigde at mitechki.net> wrote:
> James Wilkinson wrote:
> > It's usually a bit faster.
>
> Just to avoid the confusion, are you saying that 64-bit capable
> processors are faster than 32-bit only or that application compiled for
> 64-bit architecture is faster then the same application compiled under
> 32-bit architecture on the same hardware. The reply to your post tells

He probably means that a 64-bit processor is "usually a bit faster"
when running in 64-bit mode (that is, running a 64-bit OS) than in
32-bit mode.

> me that people think you mean the former, where I was talking about the
> latter. I will not dispute the claim that 64-bit CPUs are faster then
> 32-bit, cause I don't think they make 32-bit only CPUs anymore (at least
> in the x86 architecture). So any 32-bit CPU will be just plain outdated
> and therefore slower then any modern 64-bit (and 32-bit capable) CPU. As

The issue at hand is that you think running a 64-bit OS brings little
or no advantage over a 32-bit OS on a 64-bit processor unless you have
a lot of RAM or need a large address space.  Oh, and you do know it is
possible to address more than 4 GB of RAM on a 32-bit processor with a
32-bit OS, right?  Look up PAE:
http://en.wikipedia.org/wiki/Physical_Address_Extension

> for the applications, I believe the difference should be negligible
> unless the application is trying to use a lot of RAM. I think I have
> seen some benchmarks confirming this, but at the moment I cannot seem to
> find them.

There is a whole lot more to x86_64 than just addressing more RAM or
having a larger address space.  One of the biggest improvements is the
fact that it has twice as many general purpose registers (x86 has 8,
x86_64 has 16).  Whether or not an application will perform
significantly better in a 64-bit or 32-bit environment depends on the
application and what it is doing exactly.  The performance gains can
be significant, even if you do not have a large amount of RAM.  I run
x86_64 Fedora because I bought a 64-bit CPU and want to take full
advantage of my processor.

Not that this discussion is helping the OP at all...

Jonathan