[Beowulf] one vs two memory sticks

Mark Hahn hahn at mcmaster.ca
Thu May 7 14:11:26 PDT 2009

> I was wondering for a core2 machine with two ddr2 channels. What whould give
> the best preformance in term of the number of memory sticks.

the details differ, but the principle is the same for all 
computers/controllers/etc: more loads on a bus reduces its clock.
ie, putting > 1 dimm on a single channel makes it run at lower clock.

> As far as I know with core i7 it is best to put one memory stick per channel,
> but as the core2 still connects via the north side bus I was wondering if
> things are the same or whether the north side bus is the bottleneck.

the principles are the same except that the MCH typically has pretty
high drive current, and might not reduce clock for just 2 dimms.
particular MCH's vary in their drive/clock as well as how many channels.

remember that a dual-rank dimm, although only using a single slot,
counts as 2 bus loads.  (assuming it's not buffered, registered or fbdimm)

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