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From: fisher@dvinci.DEC
Newsgroups: net.space
Subject: Space Shuttle Computers
Message-ID: <2939@decwrl.UUCP>
Date: Fri, 28-Jun-85 12:00:09 EDT
Article-I.D.: decwrl.2939
Posted: Fri Jun 28 12:00:09 1985
Date-Received: Tue, 2-Jul-85 06:01:04 EDT
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Organization: DEC Engineering Network
Lines: 20

<>
> ...the fifth one is different from the other 4; it is made by Rockwell...

I could be proven wrong, but I am quite sure that all 5 cpus are the same.
The fifth one, however, was PROGRAMMED by Rockwell rather than IBM.  The 
quintuple hardware redundancy provides backup for hardware failure.  The 
separate program for #5 provides a backup for the software.

BTW, the 5 computers only run as a quintuple redundant set during critical
phases of the mission (ascent and decent, and perhaps during some of the
prelaunch activities).  At other times, they are decoupled and given separate
tasks, with only double or triple redundancy for such things as orbital
calculations, environment management, and running the arm.

Burns


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