5 ms·

Possibly talking rubbish but: a 286 is simple, well understood both in terms of its spec and its performance (no fancy pipelines, no cache, so very predictable

Possibly talking rubbish but: a 286 is simple, well understood both in terms of its spec and its performance (no fancy pipelines, no cache, so very predictable performance), is fabbed probably in the order of a micrometer so highly resistant to cosmic rays (assuming CRs do affect circuitry), inerface to memory that is equally 'boring', those 286s are perhaps hardened and quite possibly still produced for this purpose. All the above is speculation but I can imagine that I'd like very old, boring, predictable and very understood tech rather than the latest. That said, it is a bit unexpected.

Leherenn 7y ago
It's probably also certified, and has been in the 737 for a very long time. Usually, if you see something old in a plane it's a matter of certification as it's a long and really, really expensive process. If the chip has enough power to do what is needed, the only reason to change it is that procurement for new parts become more expensive than recertification. Given the price of certification, companies make sure these parts remain available for decades as that's still cheaper.
- tempguy9999 7y ago
  expensive, yah. After I posted I did a little digging. "The RAD750 is a radiation-hardened single board computer manufactured by BAE" and "The RAD750 system has a price that is comparable to the RAD6000 which is US$200,000 per board (per 2002 reference)" <https://en.wikipedia.org/wiki/RAD750> https://en.wikipedia.org/wiki/RAD750> More general info here, inc. use of an 8086 and a MIPS R3000: "The CPUs of Spacecraft Computers in Space" <http://www.cpushack.com/space-craft-cpu.html> http://www.cpushack.com/space-craft-cpu.html> which backs up the chip cost mentioned above. Generally interesting. Completely agree that if it's fast enough, why change it.

5 ms·

Possibly talking rubbish but: a 286 is simple, well understood both in terms of its spec and its performance (no fancy pipelines, no cache, so very predictable

by tempguy9999 7y ago

Leherenn 7y ago
It's probably also certified, and has been in the 737 for a very long time. Usually, if you see something old in a plane it's a matter of certification as it's a long and really, really expensive process. If the chip has enough power to do what is needed, the only reason to change it is that procurement for new parts become more expensive than recertification. Given the price of certification, companies make sure these parts remain available for decades as that's still cheaper.
- tempguy9999 7y ago
  expensive, yah. After I posted I did a little digging. "The RAD750 is a radiation-hardened single board computer manufactured by BAE" and "The RAD750 system has a price that is comparable to the RAD6000 which is US$200,000 per board (per 2002 reference)" <https://en.wikipedia.org/wiki/RAD750> https://en.wikipedia.org/wiki/RAD750> More general info here, inc. use of an 8086 and a MIPS R3000: "The CPUs of Spacecraft Computers in Space" <http://www.cpushack.com/space-craft-cpu.html> http://www.cpushack.com/space-craft-cpu.html> which backs up the chip cost mentioned above. Generally interesting. Completely agree that if it's fast enough, why change it.