Path: utzoo!attcan!uunet!csdev!ll1a!spl1!laidbak!att!alberta!ubc-cs!uw-beaver!mit-eddie!rutgers!apple!vsi1!wyse!mips!prls!pyramid!voder!kontron!optilink!cramer
From: cramer@optilink.UUCP (Clayton Cramer)
Newsgroups: comp.sys.next
Subject: Re: NeXT Memory - No Error Checking or Parity !
Keywords: Memory,errors,parity
Message-ID: <8842@spl1.UUCP>
Date: 1 Nov 88 18:55:49 GMT
References: <549@gt-eedsp.UUCP> <7493@well.UUCP>
Sender: news@spl1.UUCP
Organization: Optilink Corporation, Petaluma, CA
Lines: 43

In article <7493@well.UUCP>, ejf@well.UUCP (Erik James Freed) writes:
> I think it was Seymour Cray who was quoted as saying
> 	"Parity is for farmers"
> I would tend to support NeXT's decision. Parity is supposed to allow
> you to pinpoint where errors reside, but the software is rarely written
> so that information is easily available. In general if your system memory
> is flakey, you will soon realize that something is up and then you can
> run memory tests to isolate the particular simm module. (I assume that a
> good memory checking diagnostic will be available at a standalone level
> for the NeXT) A useable (thorough) memory test takes a lot of time. It is 
> not something that you want to run every boot up. And parity memory in
> my experience just is not really that useful. (at least to justify the PC
> real estate) I now submit myself to the flames
> Erik

ARGGGH!  I have one terribly unpleasant experience with a lack of parity,
and it makes me firm in my belief that memory needs parity.

I was writing a gas station accounting system in BASIC on a Radio Shack
Model 3 (not my choice of hardware or language, obviously), and I had
to use someone else's system for an emergency bug fix.  I loaded in
my program, edited in my changes, then saved the program back to disk.
Then I tried to run it.  And it didn't work.  Lots of variables were
undefined, and I couldn't figure out why.

After a bit of study, it turned out that bit 13 had gone bad in 16K
of RAM.  As a consequence, Q turned into A, R turned in B, S turned
into C -- and the BASIC interpreter still accepted the lines, but
all the variables were thoroughly garbled.  (The keywords survived,
perhaps using only small numbers in each word).

Fortunately, a friend drove up from Los Angeles with our master
disks, or I would have been in deep trouble.  Parity would have caught
this error, and prevented a huge loss of time and effort.

I can't take seriously a machine without memory parity.  The PC even
has parity, and there are times it has caught memory errors.  Waiting
for those errors to be obvious before searching for them is a recipe
for frustrated users, and corrupted data.

-- 
Clayton E. Cramer
..!ames!pyramid!kontron!optilin!cramer