Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!zehntel!dual!amd!fortune!wdl1!jbn From: jbn@wdl1.UUCP (John B. Nagle) Newsgroups: net.micro Subject: Parity checking Message-ID: <384@wdl1.UUCP> Date: Tue, 14-Aug-84 22:49:57 EDT Article-I.D.: wdl1.384 Posted: Tue Aug 14 22:49:57 1984 Date-Received: Thu, 16-Aug-84 03:49:42 EDT Lines: 22 Machines without parity checking must be considered only slightly above the toy level. Intermittent errors are a continual nagging problem in such machines. The IBM PC has parity checking; the PC Jr does not. The TI Professional does not, and suffers from intermittent problems because of it. Any machine costing over $1000 should unquestionably have parity checking; below that level, there is some argument for economy, but personally I would go for parity all the way down to the appliance control processor level. In a small computer general-purpose operating system, parity errors in user space should kill the job involved and display a message, not crash the machine. Parity errors in system space should crash the machine with a message. More elaborate strategies are possible; this is a minimum. Power supplies should be designed such that if the output voltage deviates from the rated value, the machine goes down. A zener in the right place will accomplish this. It is better to crash fully than have an undetected error. Again, more elaborate strategies are possible, such as power fail interrupts, but just plowing on is a bad idea. If you build an unreliable machine, it will not sell. Remember the Coleco Adam? John Nagle