A news posting about the computers used on Safeguard:

Re: Sprint missile 	
Author:	John Dierdorf
Date:	1998/06/22
On Sun, 21 Jun 1998 15:56:58, (Matthias Warkus) 
> John Dierdorf schrieb:
> > I worked on the Safeguard software from 1969 to 1975 [...]
> What was it written it? What did it run on?
Almost all of it was written in assembly language -- at the time the 
largest programming project ever written -- maybe 4,000 man-years.  
(It came in on time, on budget, and on spec, and there aren't very 
many programming projects of ANY size that did that!  And as far as we
knew it would have worked perfectly against the threat it was designed
for, ten years before!  <grin>)
The reason for ass'y was simply for speed.  As I've told a lot of my 
programming projects, the design goal was, "If we can shave another 
micro-second out of an inner loop, then we can keep 652 balls in the 
air at one time instead of 651.  Hey!  Now we can save Pittsburgh!"  
Many of the inner "loops" were NOT, in fact loops, but were written 
out linearly for speed.  (ANY tradeoff of memory for speed was 
legitimate - I can remember design-change meetings where the proposal 
was to save a millisecond.)
It ran on a multi-CPU mainframe "farm" custom-built by Univac.  Six or
eight CPUs, as I recall, with task dispatching as required.  Note that
 SMP systems weren't exactly common in the late 60's, let alone 
fault-tolerant ones.  We used to show off when the generals came 
through by asking them to disconnect any data cable or pull any power 
plug out of the wall, and the software would reconfigure on the fly 
for the loss of a CPU, memory unit, console, or whatever!!!  For 
transient errors, it could recover from an error interrupt ANYWHERE 
without a problem - and that included the first-level interrupt 
routines themselves!  IIRC, we could recover from a trap in over 99% 
of the SECOND-LEVEL interrupt-handler code! 
> I'd like all the info I can get! Can you mail me the pictures? (heavily
> compressed JPEG; if possible). And - can I put your information and the
> information of all the others as wells as the pictures and some credits lines
> in my Web page and possibly in the Safeguard FAQ?
I have the dual-sprint launch picture scanned and available at either 
1700x2700 (about 500K) or 500x800 (about 70K).  Send me an email at 
the address below and I'll send one along, along with a description of
what you're seeing.  (You can see the MSR, etc. in the picture.) It's 
public domain; in fact I have copy negatives of several pictures given
to me by the PR office.  I'm still hunting for my other prints; when I
find 'em I'll scan and maybe set up a web page.
Feel free to use anything I've said, realizing that there's somewhat 
more likelihood of error in my comments on the missile hardware, since
I was on the software side.
John Dierdorf (
Austin, TX

Last Modified: 23-Oct-1999