Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!iuvax!bsu-cs!dhesi
From: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Brown Bag Memory Test--worthless?
Summary: dynamic ram testing
Message-ID: <4795@bsu-cs.UUCP>
Date: 17 Nov 88 03:36:09 GMT
References: <4022@whutt.ATT.COM>
Reply-To: dhesi@bsu-cs.UUCP (Rahul Dhesi)
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 30

In article <4022@whutt.ATT.COM> tes@whutt.ATT.COM (STERKEL) writes:
>I ran the
>test for *10,000* iterations....
>Again,
>RAMTEST FLUNKED; finding NO-ERROR.

Dynamic RAMs of marginal quality can have defects that show up only
when a certain combination of bits is stored in adjacent cells.  To
test memory thoroughly one would have to store all possible bit
patterns.  This could take forever.  A second-best solution is to store
enough random patterns that there is a good (but not 100%) chance of
finding defects.  Perhaps in your case the program didn't test with
enough random patterns.  It might be repeating the same limited set of
patterns again and again instead of generating new ones.

I personally would be suspicious of a memory testing program that does
not document what bit patterns it uses.  Unfortunately, none of them
do.

Another possibility is that you had to disable parity checking to run
the test successfully, and so did not detect an error in the parity
bit.  (Or the program somehow disabled parity checking.  It seems to
know how to do, since it lets you do it from the screen without having
to flip a switch on the memory board.)

Aside:  There is a rumor that the reason IBM created a BCD character set
with holes was because not all combinations of on and off states in the
old transistor-based logic circuits were equally error-free.
-- 
Rahul Dhesi         UUCP:  <backbones>!{iuvax,pur-ee}!bsu-cs!dhesi