Xref: utzoo comp.sys.next:18015 comp.arch:22918
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!wuarchive!m.cs.uiuc.edu!gillies
From: gillies@m.cs.uiuc.edu (Don Gillies)
Newsgroups: comp.sys.next,comp.arch
Subject: Re: parity is for farmers?
Message-ID: <1991May25.062358.13694@m.cs.uiuc.edu>
Date: 25 May 91 06:23:58 GMT
References: <1991May21.232331.24888@cs.umn.edu> <1991May22.234515.24685@milton.u.washington.edu> <1991May23.203950.20953@zoo.toronto.edu>
Organization: University of Illinois, Dept. of Comp. Sci., Urbana, IL
Lines: 18

Actually, wouldn't it be pretty easy to provide "optional parity" on
non bank-switched memory?  At boot time, sense whether there are
parity simms installed, and if so, enable the parity checking
hardware, which uses a single simm to parity-check all the other simms
in the system.  One byte from the parity simm is used to check 8 words
of main memory.

One 4Mb simm would enough to parity-check 128Mb of memory.  If your
system was experiencing random crashes, you could install a parity
simm to detect the defective memory bank.  Once you had found the
errant memory bank, you could replace the errant part and remove the
parity simm.  This would save a lot of money, since you wouldn't
1/32th more memory on a permanent basis.

Don Gillies	     |  University of Illinois at Urbana-Champaign
gillies@cs.uiuc.edu  |  Digital Computer Lab, 1304 W. Springfield, Urbana IL

--