The rise and fall of IBM's 4 Pi aerospace computers: an illustrated history
righto.com33 points by zdw 3 hours ago
33 points by zdw 3 hours ago
Author here: I've finally finished a detailed history of IBM's 4 Pi computers, powering everything from the B-1 bomber to the Space Shuttle. Let me know if you have questions...
just one: why it named System/4 Pi ? (the Pi part especially)
The name is essentiallly a geometry joke. The IBM System/360 line of mainframes (1964) revolutionized the computer industry with the concept of one family of computers for all applications: business and scientific. (Before the 360, nobody considered compatibility, so different computer models were entirely incompatible, which was a mess.) The name symbolized that System/360 covered the full 360º of applications.
The 4 Pi name extended this idea to applications in the 3-dimensional world: 4π is the number of steradians making up a full sphere. As IBM put it, "System/4 Pi also fills a sphere—the full spectrum of military computer needs—for airborne, space, or shipboard use."
Back when I was in the USAF they told us 4 Pi was because it was essentially two IBM 360 mainframes in parallel. Probably BS but that was what we all thought.
Really happy to see this history lesson in any case, I had mostly forgotten about my experiences from the mid 90s.
You're right, that's BS :-) Yes, many of the 4 Pi systems were essentially IBM 360 mainframes; some were completely compatible, while others were more "inspired" by the 360. However, only the little-used EP/MP model was a multiprocessor system. As for the name, IBM made it clear that the name comes from 4 pi steradians in a sphere.
What 4 Pi systems did you work with, by the way? Do you have any interesting stories?
Nothing too interesting I’m afraid. The unit I was in was responsible for the 4 pi software on the E-3 AWACS. If memory serves, this was right about the time of block 30/35 rollout. I looked recently and they’re running much newer, better computers these days (it’s been 30 years, now I feel old).
We used to say that the computers were so heavy that the E-3 was routinely taking off over its maximum takeoff weight :). Another likely bit of BS. But it did take that old bird well over a minute of takeoff roll to get airborne, which is weird when you are used to airliners. I did not regularly get to ride in one, we mostly used a 4 pi in our E-3 simulator. Did a lot of “external testing” which was mostly very tedious but we did get to talk to interesting people.
The E-3's computer was definitely heavy: the brochure that I have says that it weighed 1,826 pounds. (There's a nice photo of the refrigerator-sized cabinet full of circuit boards in my article.) The 4 Pi line is kind of strange; it has all these compact 60-pound computers, and then they throw in a couple of monster systems that weigh almost a ton.