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