Compuserve also had a software dependency on the PDP-10 and Decsystem 20, and when those machines were no longer available they bought a company making clones so they could continue to manufacture them for themselves. The company they bought, Microsolutions, was Mark Cuban's first startup.
making clones of mainframes (IBM's) had been a big area of intellectual property litigation, but also facing monopolization investigations, IBM had to allow them. They were referred to as "plug compatibles".
https://www.computerhistory.org/collections/catalog/10277383... https://www.twenex.org/?network
as far as i know the control plane on their equipment is still a pdp-10 compatible
FWIW I'm developing "tiny-titan", a stand-in for Cambridge's Titan mainframe that talks to Heinz Lemke's 1972 PIXIE program over an emulated version of Neil Wiseman's PDP-7 <=> Titan link. It doesn't emulate Titan itself, just the conversation PIXIE had with it, so the unmodified 1972 PDP-7 code dials home and uploads its drawings.
https://en.wikipedia.org/wiki/Titan_(1963_computer)
>Titan was the prototype of the Atlas 2 computer developed by Ferranti and the University of Cambridge Mathematical Laboratory in Cambridge, England. It was designed starting in 1963, and in operation from 1964 to 1973.
https://news.ycombinator.com/item?id=49407938
https://news.ycombinator.com/item?id=40617894
Flight of the PIXIE - Yuja Wang:
https://www.youtube.com/watch?v=jDrqR9XssJI
UNIVERSITY MATHEMATICAL LABORATORY, CAMBRIDGE: Cambridge Supervisor - Planning Document 10 Software for the Titan/PDP-7 link:
https://cucps.soc.srcf.net/titan/supplan/pd10.htm
Here is a photo of Heinz Lemke operating PIXIE with the light pen and 340 display on the PDP-7 (also seen in the video above):
https://www.facebook.com/groups/779220482206901/posts/629772...
Ostensibly the site is about HyperTIES itself, but I'm publishing other stuff there too like a PDP-7 emulator!
https://hyperties.org/databases/pixie/pixie-live/
Here's a part of the demo I was giving at EduCom in October 1988 at the Sun booth on the trade show floor, across from the NeXT booth, where Steve Jobs and Bill Joy came by. Because he had shaved his beard, I didn't realize it was Bill Joy when I was showing him a demo of his head popping up! He took it pretty well though, better than Jobs.
https://hyperties.org/databases/playground/sun-founders-big-...
Here's a paper looking back at HyperTIES:
Cannot refrain myself from asking why ...
Time-evolution: P1 is deprecated, replaced by uncertified P2, but S1 remains certified.. just nowhere certified to run yet.
Solution: There's another software S2 which originally vouched for P1, itself still certified, which can still be used to certify P2.
Counterfactual?: If S1 were deprecated in favor of new S3.. there'd be no plan to certify it!
The problem: None of this actually makes any sense! But we're trying to fake due diligence. Everyone knows the hardware/platforms kinda need to be certified with respect to each other anyway, but if we did it that way it would all be even more expensive an time-consuming.
Particularly when the task here is "just" to measure some rod positions in a constrained 3D space ...
In a case where something is safety critical the computer is super important as very subtle errors could cause catastrophic consequences. This is why you get into things like running software on 3+ computers concurrently depending on how fail-safe something has to be.
It's not hard to imagine a similar system fabricated around an open or licensed processor core today being well within the budget of a major airline today.
Software emulation would no doubt be less expensive, but there could have been regulatory reasons for building plug-compatible hardware.
[1] https://en.wikipedia.org/wiki/PC-based_IBM_mainframe-compati...