[Gllug] Error correcting memory

[Mike Brodbelt]

On Tue, 2003-05-27 at 09:12, Tethys wrote:
> Mike Brodbelt writes:
> 
> >ECC memory is capable of correcting single bit errors.
> 
> ISTR it's capable of correcting single bit errors, and detecting
> (but not being able to fix) two bit errors.

Apparently it works by storing 64 bits of data in 72 bits of physical
RAM, with a "distance four code", and can indeed detect, but not
correct, two bit errors. This is called SECDED (single error correction,
double error detection).

More interesting, and something I didn't know until I looked on Google,
is that many motherboards with ECC capable chipsets don't actually
implement the error correction!

There's a page here that's worth a look:-

http://www.anime.net/~goemon/linux-ecc/

It lists compliant chipsets, but that is apparently no guarantee that
motherboards based on those chipsets implement the error correction:-

http://cr.yp.to/hardware/ecc.html

So it would seem that in order to get a system that does this properly,
it's necessary to verify that both the chipset and motherboard support
and implement SECDED.

Mike.





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