Newsgroups: comp.arch
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Workstation Data Integrity
Message-ID: <1990Aug10.171744.9639@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <1990Aug3.204358.330@portia.Stanford.EDU> <40694@mips.mips.COM> <2399@crdos1.crd.ge.COM>
Date: Fri, 10 Aug 90 17:17:44 GMT

In article <2399@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
>| Most PCs (including the MACs I've seen) don't have or at least
>| don't use parity.
>  The IBM PC, AT, and PS/2 models use per-byte parity, as do all of the
>clone machines built by other vendors. This provides adequate
>protection... The term PC includes both business PCs, with minicomputer
>features, and machines intended primarily for games and home use, which
>are built as cheaply as possible...

But, but, but... virtually all MSDOS software *explicitly ignores*
parity errors.  A friend of mine, working for a clone builder, had
an interesting story to tell.  They were horrified to discover that
their parity circuit didn't work... after a good many of the machines
were in the field and functioning fine!  It hadn't been caught in
the factory because there is no way that software can test the IBMPC
parity system, and it hadn't been caught by the customers because all
the commercial software just ignored it.

People who think their MSDOS "business PCs" are somehow "protected"
against memory errors by the parity hardware are kidding themselves.
-- 
It is not possible to both understand  | Henry Spencer at U of Toronto Zoology
and appreciate Intel CPUs. -D.Wolfskill|  henry@zoo.toronto.edu   utzoo!henry