[Beowulf] Re: Beowulf Digest, Vol 10, Issue 16
hahn at physics.mcmaster.ca
Tue Dec 14 12:05:25 EST 2004
> Back to the original thought, which was recycling the PC2100
> memory from the Tyan S2466N boards. The consensus seems to be that
> registered ECC recycled from the S2466N systems will not work in
> boards designed for unbuffered ECC, which means that both
> the 754 and 939 are out.
I believe the relation is the other way: you cannot use unbuffered
dimms in a board which assumes buffered dimms. that is, the dependecy
is based on what fanout the drivers can handle: unbuffered dimms
have more devices hanging off the same signals. I don't think there's
a difference in pinout.
note that sidedness of the dimm also matters (some dimm vendors
call double-sided dimms "dual-rank".
> Very unclear to me what, if anything is gained by using
> registered ECC vs. unbuffered ECC on a smallish system. On a big
1 clock latency (actually, I think it's a major cycle, so for ddr,
it's the equivalent of two transfers) overhead for registered dimms
(theoretically, there are also buffered dimms which have pass-through
tranceivers which mitigate the drive/fanout problem, but don't
impose a whole cycle latency. but I think no one does that anymore.)
> be a plus. But if the system only holds 1Gb of RAM in one
> or two memory slots the unbuffered memory should be slightly
> faster, and with the ECC enabled, just as reliable. Correct?
that's my understanding...
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