Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!necntc!encore!chan
From: chan@encore.UUCP (Jerry Chan)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Problem with disk I/O in turbo mode
Keywords: parity check error
Message-ID: <3194@encore.UUCP>
Date: 11 Jun 88 18:25:58 GMT
References: <1050@klipper.cs.vu.nl>
Reply-To: chan@encore.UUCP (Jerry Chan)
Organization: Encore Computer Corp, Marlboro, MA
Lines: 44

In article <1050@klipper.cs.vu.nl> beugel@cs.vu.nl (Beugel BJ) writes:
>- 640 K, 150 ns, parity checked main memory;
>The problem is as follows:
>
>In slow 4.77 MHz mode I have no problems whatsoever.
>In 8 Mhz turbo mode however, the system hangs when I
>try to save or copy a large file (e.g. 140 K) on the
>hard-disk from within WordPerfect.
>The screen is cleared except for an error message
>saying "PARITY CHECK 200000 (S)" which is obviously not a

You've got to be careful when using 150nsec parts while running
0 wait states at 8mhz.  You really should be using 120's to be safe.
Year(s) ago, when memory was bountiful and cheap, lots of Japanese
chips were used;  nowadays, Japanese chips are hard to come by, and
as a result, American chips are used.  It turns out, in my experience,
that the margins on the Japanese parts tend to be much better than
the American counterparts, i.e., 120nsec NEC's work where the same
TI parts fail.  The problem comes when the systems integrators try
to substitute the "slower" American chips for the Japanese counter-
parts.  Should work, but experience has shown otherwise.

The problem with marginal memory chips is that it is extremely
difficult to isolate the problem -- the system may fail lots of
different ways.  Ways to find out:  (1) Substitute chips with
faster ones (laughter and jeering in background -- $$$);  (2)
Run your system at a slower clock; (3) run your system with an
added wait state (jumper on motherboard, keyboard combo, ...).
If your system works when in any of these other modes, the ram can
be considered suspect.

One more thing -- this would help provide further insight to find
the problem:  is your system new?  Has it ever been able to run
the programs which now fail?  If it was able to run the mentioned
programs, what is different now than before (hardware, software)?
You may want to back off on any changes you'd made to the system
to see if the problem goes away.

Hope this helps --

   +----------------+  Jerry H. Chan                linus--+
+--+-------------+  |  Encore Computer Corp.       necntc--|
|  | E n c o r e |  |  257 Cedar Hill St.           ihnp4--+-encore!chan
|  +-------------+--+  Marlboro MA 01752           decvax--|
+----------------+     (617) 460-0500             talcott--+