[Beowulf] Opteron performance

Bill Broadley bill at cse.ucdavis.edu
Wed Dec 8 01:08:46 PST 2004

On Tue, Dec 07, 2004 at 03:36:30PM -0800, Joel Jaeggli wrote:
> On Tue, 7 Dec 2004 pesch at attglobal.net wrote:
> >Where can I find a decent comparison betwenn Opteron and Athlon64
> functionaly the only difference betten the two is memory bandwidth and the 
> number of ht ports.

Er, it's a bit more complicated than that.

Athlon 64's are available in 3 flavors:
s754 athlon 64s have a 64 bit memory bus (unregistered memory, 1 less cycle)
s939 athlon 64s have a 128 bit memory bus (unregistered memory, 1 less cycle)
s940 athlon 64s have a 128 bit memory bus (registered, 1 more cycle)

The FX is available in both s939 and s940, but are "unlocked" so you
can change the multiplier (useful mostly for overclocking).

Athlon 64s have 2 cache sizes, 512K and 1024K.  Be careful often the
same cpu rating (like the athlon 64 3200) are available in 2 cache sizes
and 2 clock speeds.

So the main performance differences are 1/2 the memory bandwidth for
s754 chips, and 1/2 the cache size for some athlon 64's.  The effect
of either will depend on the application.

AFAIK, the s939 athlon 64's have 3 HT's just like the opteron, but none
of them are coherent, so you can't run SMP with them.

Bill Broadley
Computational Science and Engineering
UC Davis

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