[Beowulf] Better C2D or Quadcore

[Mark Hahn]

>   - high per-CPU memory performance. Each CPU (core in dual core
>   systems) needs to have its own memory bandwith of roughly 2 or more
>   gigabytes. For example, standard dual processor "PC's" will
> notprovide better performance when the second processor is used, that
> is, you
>   will not see speed-up when you using the second processor. This is because
>   the speed of sparse matrix computations is almost totally determined by the
>   speed of the memory, not the speed of the CPU.

which argues against quad-core Intel, and _for_ dual-socket AMD machines.
our experience is that petsc really does like local memory bandwidth,
though I'm sure you can use it in programs which are cache-friendly if 
your data is small enough.  I haven't noticed petsc programs being especially
hard on the interconnect (our petsc users seem as happy with myri 2g as with
quadrics elan4 - our Gb cluster is mainly for serial.)