> > Fry's (a big local discount computer & electronics chain) has a great
> > deal on build-it-yourself Athlons (US$ 350 for 1.2GHz CPU, MB, case,
> > floppy, ethernet card, 56K modem & video card) so I'm going to take
> > the plunge.
those motherboards in those starter kits tend to be JUNK.
...
> > The one question that remains is whether to buy ECC or
> > non-ECC memory? Neither is terribly expensive (256MB of
> > Athlon-compatible PC133 memory goes for $45 non-ECC, $90 ECC at
> > pricewatch.com), but I don't want to pay extra unless I'm sure it will
> > give some definite advantage. So the question is: does ECC memory of
> > this kind actually do active error correction, or merely detection?
Does the mobo even support ECC? Its a function of the chipset *and* the
system BIOS. I'm not aware of any VIA type motherboards having any sort of
parity or ECC capability.
> Actually there are several questions here...
>
> Memory described as ECC should actively correct single-bit errors and
> detect most multi-bit errors. If an uncorrected error is detected, it
> should raise non-maskable interrupt, which (depending on the OS) will
> probably cause a kernel panic (or BSOD on a Windows system).
> If an error is detected and corrected, the memory should raise a
> different interrupt, which the OS may ignore, or log somewhere.
The standard for Hamming code based ECC is correct single bit, and detect
double bit errors. more than 2 bits wrong will probably have a ~50% chance
of being caught, or possibly mask as a different single bit error and get
incorrectly corrected. An uncorrectable error will be treated as a parity
error, and either hard halt the box, or cause an abrupt reboot.
> My understanding is that the correction is actually done in the DIMM
> itself, but depends on the appropriate signals being supplied by the
> chipset.
No, the correction is done in the chipset. the ram is simply 72 bits
instead of 64 bits wide
enabling ECC generally adds a clock penalty to every write too, so it slows
things down considerably.
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