Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!rice!hypatia!phil
From: phil@hypatia.rice.edu (William LeFebvre)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle Computer Info?
Message-ID: <3227@kalliope.rice.edu>
Date: 5 May 89 21:04:29 GMT
References: <24055@agate.BERKELEY.EDU>
Sender: usenet@rice.edu
Reply-To: phil@hypatia.rice.edu (William LeFebvre)
Organization: Rice University, Houston
Lines: 45

In article <24055@agate.BERKELEY.EDU> labc-4da@e260-4d.berkeley.edu (Bob Heiney) writes:
>What kind of information can I get on the design, implementation, etc. of
>shuttle software?  Is there someone I should write?
>
>I'm interested in this info at almost any technical level, though source
>code (in Fortran?) would be a little much.  :-)

Well, I happen to have access to someone who knows a great deal about the
on-board computer system.  You didn't really specify, but I assume that
you are referring to the software that's used in the on-board computers
(the General Purpose Computers, or GPC's).  Correct?

I don't know how much I can find out about the history of the programs
(design and implementation issues), but I can get an answer for just about
any technical question concerning the GPCs.

I'll tell you what I know about them off the top of my head:  there are
five General Purpose Computers (GPC) on board.  The hardware in each GPC
is identical:  it is an IBM AP-101/B computer.  Typical IBM segmented
architecture, but memory is addressed on 16-byte boundaries (IBM calls
them "half-words", the rest of the world calls them "words" or "shorts").
Each GPC has 212 half-words of iron-ferrite core (yes, iron-ferrite core)
memory (that's the equivalent of 424K).

Nominal ascent and entry configuration has GPCs 1 thru 4 running the
primary flight software and GPC 5 running "BFS", the backup flight
software.  The primary software was written by IBM, BFS was written by a
team at Rockwell.  The primary software controls all the flight critical
stuff, the BFS just calculates and only goes into action if it is needed.
Only the commander and pilot can make the decision to switch to the BFS
(it will never happen automatically), and that has never happened in a
real flight.  All the software was originally written in HAL/S, some weird
almost-structured algol-like language.

What else do you want to know?

			William LeFebvre
			Department of Computer Science
			Rice University
			<phil@Rice.edu>

P.S.: at one point (long ago) the wonderful media was misinforming the
public by saying that "four computers were built by IBM and one was built
by Rockwell".  Don't believe it.  It's the software that's different,
*not* the hardware.