Path: utzoo!utgpu!watmath!att!pacbell!noe!marc
From: marc@noe.UUCP (Marc de Groot)
Newsgroups: comp.unix.microport
Subject: Re: NMI in System Mode on System V/386
Message-ID: <645@noe.UUCP>
Date: 3 Jul 89 08:24:22 GMT
References: <781@cgh.uucp> <143800004@cdp>
Sender: usenet@noe.UUCP
Reply-To: marc@noe.UUCP (Marc de Groot)
Organization: Noe Systems, San Francisco
Lines: 33

In article <143800004@cdp> dfriedlander@cdp.UUCP writes:
>It's true, diagnostics don't seem to pick up all memory problems.  
>My AST386C ran fine under DOS (5MB memory.)  Indeed, not only did
>diagnostics show no problem, but I was able to fill up all the memory
> [ ... ]
>I wonder if anyone understands why this sort of weirdness happens.

Memory tests which REALLY test memory are not as easy to write as they
might appear.  There are quite a variety of problems which cause memory
to fail.

Any memory error where a bit a just STUCK was detected when your machine
was burned in.  In other words, the manufacturer got all the EASY problems.

Your memory probably works 99.9% of the time -- it's a very occasional
bad write of a bit that is causing the failure.

The memory test that the PC does at power-on is hopelessly ineffective
at catching marginal memory errors simply because it does not test the
memory long enough, and because it does not vary the patterns that it
writes.

Back in prehistoric times, when I had a S-100 bus machine with a Z80,
we had the "Rasmussen memory test" which had a good-sized repertoire
of different memory tests that it would run.  I would leave it running
for HOURS to catch marginal memory.  I haven't seen anything like this
for PC's.

-- 
Marc de Groot (KG6KF)                   These ARE my employer's opinions!
Noe Systems, San Francisco
UUCP: uunet!hoptoad!noe!marc
Internet: mdg@postgres.berkeley.edu -or- marc@kg6kf.AMPR.ORG