Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!netnews.upenn.edu!linc.cis.upenn.edu!rubinoff
From: rubinoff@linc.cis.upenn.edu (Robert Rubinoff)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle computer reprogramming
Keywords: shuttle, wind, programming
Message-ID: <5383@netnews.upenn.edu>
Date: 30 Sep 88 15:57:54 GMT
References: <6689@nsc.nsc.com> <1543@hp-sdd.HP.COM>
Sender: news@netnews.upenn.edu
Reply-To: rubinoff@linc.cis.upenn.edu.UUCP (Robert Rubinoff)
Organization: University of Pennsylvania
Lines: 23

In article <1543@hp-sdd.HP.COM> hinojosa@hp-sdd.hp.com.UUCP (Daniel Hinojosa) writes:
>Someone here at work mentioned that the shuttle has less memory than
>many home computers, in the neighborhood of 640K. Let's assume for
>now that this is the case. Not only does that seem like an amazingly
>low amount of memory to help resolve such issues, but it seems like
>it could easily be an item that might have been considered for improvement
>after the Challenger incident. 
>

Part of the problem is that the shuttle uses magnetic core memory (remember
that?) because it's non-volatile.  In fact, I believe they always load the
next program they're going to use into the computer as soon as they're done
with the current one, so that if they have problems, as soon as they get the
computers back up they'll be ready to run.

There was a long case study of the shuttle computer systems a few years ago
in the Communications of the ACM.  The computers are actually fairly old
technology all around; they're special purpose versions of IBM 360 processors.
They wanted technology that had been extensively tested over a long period
of time, since it would be difficult to get a service rep up to the shuttle
in case of trouble.  

   Robert