ECC memory

[Mark Hahn]

> motherboards don't seem to have ECC support.  I've seen all sorts of
> conflicting accounts, but it seems to be the case that there is no ECC
> support with these boards. 

I just looked at the kt133a datasheet, and it doesn't mention ecc support.
the kt266 blurb *does* claim ECC support, though.

> The odd thing is, I've seen several companies
> selling their commercial Beowulf systems with KT7(A) mobos and ECC
> memory.  Since non-ECC motherboards can sometimes use ECC memory with the
> ECC functionality disabled, are these companies just fooling people by
> selling ECC memory along with boards that can't use ECC?  

looks like it.

> For me, this also brings up the question of how ECC works.  Does the DRAM
> module perform the error correction, or does the chipset perform error
> correction?  From some research and common sense, it seems the chipset
> does it - otherwise, what's the point of bringing the extra 8 ECC lines
> off of the memory chip?

the chipset does it.

> Finally, have people found ECC to even be necessary?  From some of the
> stats we've seen, it seems like ECC is the way to go.  But it also seems

what stats are those?  it's difficult to find the relevant data, namely
the FIT (failures in time) statistics for a given dram chip.  the last time
I saw any was a few years ago when Intel introduced a chipset with no ECC
support.  at the time, they circulated a whitepaper containing FIT numbers
to prove that with expected ram size and use, ECC was not overboard.

you must remember that ECC costs at least 12.5% more (usually 20-25%),
*and* consumes a clock cycle of latency.

whether ECC is right for you depends mainly on the amount of ram and how hard
you use it.  possibly also environmental factors (altitude, etc).  most
people *do*not* argue for skipping ECC by saying "oh, my data is junk, I don't 
care about a few flipped bits".

regards, mark hahn.