Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!amdcad!ames!pacbell!att!ihlpl!knudsen
From: knudsen@ihlpl.ATT.COM (Knudsen)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle computer reprogramming
Summary: Memory, so they say
Keywords: shuttle, wind, programming
Message-ID: <6980@ihlpl.ATT.COM>
Date: 30 Sep 88 16:51:17 GMT
References: <6689@nsc.nsc.com>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 23

Well, the network (ABC) said it was memory limitations.
The computers each have at most 512K each (they never said exactly),
maybe only 256 or 64K.  I gather the programs are comp9led with
a #define WIND_SPEED 12345 or some such thing becasue there's no
room for a routine to read the stuff in.  Probably so little
space that a "load immediate #speed" instruction was needed,
rather than "load address from table."

The PBS station did a special last nite on the shuttle.
One of the flight crew said that every time they want to
put a new capability into the computers (like yet another
emergency abort scenario), something else has to be
taken out.  Like choose which emergency procedures you
want this time.

So I'll bet every byte of that code is hand-optimized
to hell and back.  I doubt any hi-level language,
or even C, got anywhere near those computers.

Would someone who knows like to tell us how much RAM & ROM
these babies have?  I know they use core memory (a good
idea in some senses).  Also what CACM issue described them
(around 1982 I think)?