[Beowulf] power usage, Intel 5160 vs. AMD 2216

[Mark Hahn]

> chipset(s), inefficiency in the power supply, and the memory. On thing that 
> surprised me a bit the last time I looked at this a year ago was that the 
> power use of typical memory sticks is quite high, often more than 10W. In

do your systems use very large numbers of dimms?  I think ours are 
typically 4-8.  so even 8x10W is going to be comparable to a cpu
or the inefficiency of a mediocre PSU.

like most of these other factors, this is a situation that's improving - 
one of ddr3's main changes is going from 1.8 to 1.5V, saving ~30% on power.

one nice thing is that dram dissipate a lot less power when fully-on
but not continuously bursting (~50 mA vs 300).  I don't know whether current
bios/mem controllers will but dram into the really low-power modes (~7mA 
self-refresh) by default.

> fact if you look at system with well-designed cooling, you'll see that the 
> fans are designed to blow a lot of air over the memory area.

yes, though the power density is relatively low.  I wonder if one could 
come up with a specific access pattern that would overheat particular 
chips on a dimm - perhaps even corresponding chips on a dual-rank dimm...