Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site wdl1.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!uw-beaver!tektronix!hplabs!hpda!fortune!wdl1!jbn From: jbn@wdl1.UUCP Newsgroups: net.micro Subject: Re: EPROM memory lifetime query Message-ID: <649@wdl1.UUCP> Date: Thu, 22-Aug-85 20:23:40 EDT Article-I.D.: wdl1.649 Posted: Thu Aug 22 20:23:40 1985 Date-Received: Sun, 25-Aug-85 13:14:05 EDT Sender: notes@wdl1.UUCP Organization: Ford Aerospace, Western Development Laboratories Lines: 15 Nf-ID: #R:wdl1:-56200:wdl1:1400065:000:730 Nf-From: wdl1!jbn Aug 19 11:55:00 1985 ``EPROMS retain their data indefinitely''. Wrong. Fuse-blowing PROMS may retain their data indefinitely, but the UV-erasable jobs do eventually discharge. These are capacitors. Also, a random failures per unit time model is incorrect here. Think of a RC circuit slowly discharging; R is very high but not infinite. When the stored voltage drops below some threshold, the bit is gone. But how long does this take? The question is, can we put spare boards with EPROMS in them in dead storage and expect to use them a decade or two later? This has implications for any system with a long lifespan. Usually we expect the spares to live longer than the units in use; that may not be true here. John Nagle