Mepis is built for 32-bit x86, so on the AMD 64 bit processors, it runs 
as a 32-bit system.  AMD made the right choice here by choosing to make 
their 64-bit system completely compatible with 32-bit x86 software, so 
systems that assume the AMD is a plain Pentium work just fine.

On recompilation:
In order to have your system actually work as a 64-bit build, you 
actually have to recompile everything, kernel, all of the GNU tools, 
your favorite applications, etc... for 64-bit, and a lot of apps don't 
compile this way yet.  For apps you leave as 32-bit binaries, you need 
to set up one of several supporting regions for them to run with that 
contain the 32-bit system libraries, etc...  Some builds go full 64-bit 
and set up a chroot "jail" where 32-bit apps run, others set up a kind 
of library sharing scheme (which has it's own problems at times).  I'd 
recommend picking up a pre-built 64-bit distro, since just recompiling 
the kernel for 64-bit will, usually, break just about everything on the 
system (I had this happen with a Mepis install a while back).

good luck.

==Joseph++

Eric "Shubes" wrote:

> Craig Brooksby wrote:
>
>>
>> Here's a dumb question for you hard core Linux types:  I am a "Desktop
>> Joe" running Simply Mepis on an Athlon 64 box I just built.  I assume
>> that Mepis treats it as a generic X86 processor.
>
>
> I don't know, but that would be my guess too.
>
>> So: do I need to /
>> should I recompile from source, in order to gain what -- performance? 
>> stability?  I have looked, but haven't found resources relating
>> specifically to Linux and Athlon 64 so perhaps it's a non issue.  Any
>> advice will be appreciated.
>>
>> Thanks --
>> (the other) Craig
>
>
> Recompiling the kernel source isn't trivial (unless of course you've 
> done it once or twice). To KISS, I'd try a distro that is precompiled 
> for the AMD64, such as Fedora Core 3 at 
> http://fedora.redhat.com/download/
>