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From: dricejb@drilex.UUCP (Craig Jackson drilex1)
Newsgroups: comp.arch
Subject: Re: Workstation Data Integrity
Message-ID: <14623@drilex.UUCP>
Date: 12 Aug 90 00:21:11 GMT
References: <1990Aug3.204358.330@portia.Stanford.EDU> <40694@mips.mips.COM> <2399@crdos1.crd.ge.COM> <1990Aug10.171744.9639@zoo.toronto.edu>
Organization: DRI/McGraw-Hill, Lexington, MA
Lines: 53

In article <1990Aug10.171744.9639@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
|In article <2399@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.com (bill davidsen) writes:
|>Someone else wrote:
|>| 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.

While this may be a good story, I've never truely heard of software routinely
disabling the parity check, or the NMIs it reports.  Although I have
not been associated with any mainstream applications, I know that nothing
my company has delivered disables NMIs.  There's really no reason to--
the 16k, 64k, and 256k chips used in most PCs just don't have that many
errors.  Lots of people will report that they have seen a parity error
message from a PC, but only rarely.

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.

|People who think their MSDOS "business PCs" are somehow "protected"
|against memory errors by the parity hardware are kidding themselves.

Admittedly, modern computer users (both businesspersons and engineers)
rarely view their hardware with the skepticism that it deserves...
They haven't lived through the era of "If you don't like the answers,
run it again.  They might change."  (CDC 6400, circa 1976)

|-- 
|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

On this, I agree with Henry.  Anybody who claims to appreciate the 80x8x
line of Intel CPUs needs education, medical attention, or both.
-- 
Craig Jackson
dricejb@drilex.dri.mgh.com
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