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Date: Sat, 25 Oct 1997 23:10:49 -0400
From: Jerry Hicks <wghhicks@ix.netcom.com>
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To: Mike Smith <mike@smith.net.au>
CC: freebsd-hackers@freebsd.org
Subject: Re: Parity Ram
References: <199710260126.LAA00539@word.smith.net.au>
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Mike Smith wrote:
> 
> > Yeah, but when you go to buy memory they have ECC *OR* parity types
> > available. ECC generally costs more than parity...
> 
> Crap.  In the case of 72-pin parts, parity and ECC are both x36.  30-pin
> parts are either x8 (no parity) or x9 (parity, or ECC in groups of 4).
> 
> mike

Hi Mike,

i understood that they're referred to as ECC vs PARITY because of the
memory controller interface. True, the same number of bits are found in
devices labeled both ways.

Some ECC controllers must have special requirements of the interface to
the memory (timing, interleaving ?)

A quick AltaVista search on ECC found this link: 

http://www1.ibmlink.ibm.com/HTML/SPEC/6062ipme.html#pari

(IBM, ugh) In this example they are pretty explicit that parity memory
is different from ECC-EDO devices.  i'll bet the prices are different
too.

i'm really just trying to understand all this myself; i'm not a hardware
type. (heck, i'm not that much of a software type either ;)

Do you know anything of Richard Hamming's assertion that parity memory
(the old fashioned even/odd type) is-a-bad -thing in large
configurations?

this is bound to be a FAQ...

Thanks,

Jerry Hicks
jerry_hicks@bigfoot.com