Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 7/1/84; site amd.UUCP
Path: utzoo!watmath!clyde!burl!amd!phil
From: phil@amd.UUCP (Phil Ngai)
Newsgroups: net.micro
Subject: Re: Is parity *really* worth it?
Message-ID: <155@amd.UUCP>
Date: Thu, 2-Aug-84 13:08:47 EDT
Article-I.D.: amd.155
Posted: Thu Aug  2 13:08:47 1984
Date-Received: Sat, 4-Aug-84 00:01:36 EDT
References: <586@sri-arpa.UUCP>
Organization: AMD, Santa Clara, CA
Lines: 27

There are two arguments here:

1) Parity decreases your MTBF and increases your cost. It decreases
your MTBF because it adds more parts which can break. (please, no
flames yet) It increases your cost by more than just a couple of DRAM
chips. You also need 2 parity generators, the logic which detects
a parity fault at an appropriate time for sampling and can remember
the fault until told to forget, a free interrupt line, and logic
to force a parity error so you can verify the parity detectors work.
This is typically about 8 chips worth. I should know, I designed
parity into my last product. At the time I did not feel it was worth
it but the customer demanded it.

2) What if you get a soft error in your RAM and your data is corrupted.
How much is that worth? Although parity decreases the MTBF it increases
your confidence factor. One can argue that soft errors only happen
a few times a year but in many applications that is a big problem.

I find all this very interesting because I am at a stage where I can
implement or not implement parity in my current project. I haven't
decided yet.

-- 
 I'm going to keep boring until I strike oil.
 Phil Ngai (408) 982-6554
 UUCPnet: {ucbvax,decwrl,ihnp4,allegra,intelca}!amd!phil
 ARPAnet: amd!phil@decwrl.ARPA