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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