Adrian (a.delete@this.acm.org) on January 3, 2021 1:14 pm wrote:
> Tim McCaffrey (timcaffrey.delete@this.aol.com) on January 3, 2021 9:28 am wrote:
> >
> > Parity existed on every motherboard until EDO DRAM got introduced.
> > I think there were a couple of factors:
> > 1) EDO DRAM, IIRC, was produced in a x8 package only, there was no x1 (or x9) package.
> > (This made adding a parity bit difficult).
> > 2) ECC is a pretty big step up (when EDO was introduced) in the memory controller,
> > easier to just not include it.
> > 3) At the time EDO was introduced, memory was very expensive (I paid $300 for 8 Meg
> > at that point in time, of course memory prices crashed right after that :( ).
> > 4) Once motherboard & memory controller (north bridge) vendors got away without supporting
> > parity for a couple of years, everybody was cutting that corner to stay competitive.
> >
> > ECC was first available in servers because customers demanded it.
> > I'm not sure, to this day, how much the various OSes actually support reporting
> > ECC corrections or how proactive they are isolating questionable memory.
> > I know the mainframes I worked on were able to hot swap out bad memory, which was
> > a big selling point (and required lots of OS support). Of course, these days
> > you can just migrate the VM to another host, but you still need to be able to
> > flag when bad things are happening.
>
>
> I have actually used 16 Mbytes of EDO memory with parity on my Pentium motherboard. Unfortunately,
> the motherboard used the evil Intel Triton chipset, which did not check the parity.
>
>
> I had bought the memory before the motherboard. The new Intel policy
> of omitting error detection support was a surprise for me.
>
> The EDO modules with parity (4 Mbyte per module, with 5 packages on a single
> side) used one smaller x4 memory package for each 4 larger x8 packages.
>
>
> Many of the other EDO modules that I have seen, without parity, had in fact the same PCB layout as
> my modules with parity, except that the central small x4 package was not soldered on the modules.
>

I think ECC was designed specifically so that obsolete x1 and "quad CAS" chips would not be needed unlike with parity. Even before Triton PC OEMs was already eliminating parity on desktop PCs.