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I have a document on my bookshelf a few feet from here comparing the 386 to the 486 for space mission purposes. Its core conclusion was that the 486 on-die cach

I have a document on my bookshelf a few feet from here comparing the 386 to the 486 for space mission purposes. Its core conclusion was that the 486 on-die cache was not spaceworthy and that with it disabled integer math was not really faster than on the 386. The recommendation was to use the 386+387+plus an external cache, partly because compilers for the 486 all optimized for that internal cache and compiled code poorly with it disabled, even if adding external cache. Putting computers in space is not a simple thing, of course. Such documents as this point out some of the difficulties. "Analysis of the Intel 386 and i486 microprocessors for the Space Station Freedom Data Management System" Yuan-Kwai Liu NASA May, 1991 RTOP 488-51-01 ISBN 9781729173374 https://www.libreriauniversitaria.it/analysis-intel-386-and-i486/book/9781729173374 https://www.libreriauniversitaria.it/analysis-intel-386-and-...

giantrobot 4y ago
That's interesting as the ISS (née Freedom) did in fact go with rad hard 386s for the MDMs (multiplexer-demultiplexer). These are the general purpose computers that connect dumb devices on the station like sensors or actuators to the station's main data bus. As for why Freedom/ISS went with 386s for the MDMs, I don't personally know. I'd guess that of the rad hard chips various defense companies shipped, a 386 was one of the more powerful. AFAIK the likes of the hardened RCA 1802 and some other 8-bit CPUs were pretty popular in the defense space. The RCA 1802 was used on a lot of the NASA's New Frontiers program probes. The MDM design on Freedom/ISS was meant to have a standardized component that was easily replaceable and use software to define the role of the device. An MDM plugged into a pump actuator today could have its EEPROM flashed and be plugged into a pressure sensor tomorrow. A useful feature in a system humans live in. That doesn't change the fact NASA's been RISC-y with their probes for the past three decades. The added power of the CPU (whatever the architecture) in today's probes means fewer specialized chips like were needed in older probes. That means more of the mass budget can go to science instruments and software can do the jobs that used to require dedicated chips. For anyone interested you can get the paper from NASA here[0]. It's pretty interesting. Thanks for pointing it out. [0] https://ntrs.nasa.gov/citations/19910016373 https://ntrs.nasa.gov/citations/19910016373

giantrobot 4y ago

That's interesting as the ISS (née Freedom) did in fact go with rad hard 386s for the MDMs (multiplexer-demultiplexer). These are the general purpose computers that connect dumb devices on the station like sensors or actuators to the station's main data bus. As for why Freedom/ISS went with 386s for the MDMs, I don't personally know. I'd guess that of the rad hard chips various defense companies shipped, a 386 was one of the more powerful. AFAIK the likes of the hardened RCA 1802 and some other 8-bit CPUs were pretty popular in the defense space. The RCA 1802 was used on a lot of the NASA's New Frontiers program probes. The MDM design on Freedom/ISS was meant to have a standardized component that was easily replaceable and use software to define the role of the device. An MDM plugged into a pump actuator today could have its EEPROM flashed and be plugged into a pressure sensor tomorrow. A useful feature in a system humans live in. That doesn't change the fact NASA's been RISC-y with their probes for the past three decades. The added power of the CPU (whatever the architecture) in today's probes means fewer specialized chips like were needed in older probes. That means more of the mass budget can go to science instruments and software can do the jobs that used to require dedicated chips. For anyone interested you can get the paper from NASA here[0]. It's pretty interesting. Thanks for pointing it out. [0] https://ntrs.nasa.gov/citations/19910016373 https://ntrs.nasa.gov/citations/19910016373