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From: douglas%cirrusl@oliveb.ATC.olivetti.com (Douglas Lee)
Newsgroups: comp.arch
Subject: Re: Workstation Data Integrity
Message-ID: <2372@cirrusl.UUCP>
Date: 7 Sep 90 15:25:14 GMT
References: <19208@dime.cs.umass.edu> <1990Sep6.141040.3244@mozart.amd.com> <2496@crdos1.crd.ge.COM> <1990Sep7.003451.13193@portia.Stanford.EDU>
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In <1990Sep7.003451.13193@portia.Stanford.EDU> dhinds@portia.Stanford.EDU (David Hinds) writes:

>   But don't you really only need one parity bit per word, if you only
>want to be able to detect single bit errors?  Using one parity bit
>per byte is wasteful - which is why the EDAC looks good.  Having one
>parity bit per 64 bit word would seem to be the more fair comparison.
>Using 8 parity bits per word amounts to catching most two-bit errors
>as well - but catching more than single bit errors is not what parity
>is tailored for.

> -David Hinds
>  dhinds@popserver.stanford.edu

But using byte parity allows you to do things like byte writes. If you
use word parity, you must do a read modify write for every byte in
order to update the parity of the word. This is very inefficient.

Douglas Lee