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From: hankd@dynamo.ecn.purdue.edu (Hank Dietz)
Newsgroups: comp.arch
Subject: Re: Workstation Data Integrity
Summary: credit where it's due
Keywords: Partiy checking
Message-ID: <1990Aug20.151438.27121@ecn.purdue.edu>
Date: 20 Aug 90 15:14:38 GMT
References: <1990Aug3.204358.330@portia.Stanford.EDU> <40694@mips.mips.COM> <2399@crdos1.crd.ge.COM> <1990Aug10.171744.9639@zoo.toronto.edu> <14623@drilex.UUCP>
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Organization: Purdue University Engineering Computer Network
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In article <14623@drilex.UUCP> dricejb@drilex.UUCP (Craig Jackson drilex1) writes:
>In article <1990Aug10.171744.9639@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>|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!
...
>While this may be a good story, I've never truely heard of software routinely
>disabling the parity check, or the NMIs it reports.

Ignoring interrupts used to be the norm back when polled I/O was
common.  Many micros ran with interrupts disabled because they could
interfere with the activities of some "dumb" floppy disk controllers,
etc., which depended on timing of memory accesses (e.g., the old
NorthStar floppy disk controller and their BCD floating point board).

...
>Parity in "personal" computers was one of the innovations of IBM--their
>corporate standards required it.  Up until the PC came out, hardly any
>of the computers sold as "personal" computers (Apples, CP/M boxes) had
>parity.  I'm not sure if even the contemporary Unix boxes (Onyxs) did.
>The PCjr was the first computer IBM ever shipped without parity--I'm sure
>that the angst nearly killed somebody.

Not so.  Lots of CP/M machines had memory boards with byte parity long
before the IBM PC.  Note that I'm not saying people used it -- in
fact, I vaguely recall at least one board which had sockets for parity
RAM, but standardly came with that portion of the board unpopulated.
Of course, one could argue that before the IBM PC, "hardly any"
microprocessor-based computers of any kind were sold.  ;-)

BTW, none of old machines I've played with has ever had a parity error
(i.e., bad RAM chip), although I've seen a fair number in newer
machines.  Remember the days when companies used to actually test
machines *BEFORE* shipping them...?  ;-)

						-hankd@ecn.purdue.edu