Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Continue with learning C |
| Date | 2016-09-18 20:36 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87k2e9j8ze.fsf@bsb.me.uk> (permalink) |
| References | (6 earlier) <8b6d5227-f102-4ca9-b964-45b65485c2dc@googlegroups.com> <nrkm32$dj4$1@dont-email.me> <nrm8ss$dki$1@dont-email.me> <nrmcav$p43$1@dont-email.me> <e47tq7Fjvn0U1@mid.individual.net> |
"Osmium" <r124c4u102@comcast.net> writes: > "BartC" wrote: > >> Didn't the Space Shuttle have multiple backup computers, one of >> which was programmed by a different team to make sure they didn't >> share the same bugs? > > I don't think I ever heard that before, but if so, it could lead to > some nasty side effects. > > Imagine being on the shuttle and knowing you are going to die in a > little while if you react wrongly. Computer A says do X and computer > B says do Y. What a terrifying way to die. The main flight system was designed for four or five computers (you get two failures with five and can still get a single result by majority vote) but the result of the synchronised computations are presented as definite actions -- the shuttle turns, it's engines fire and so on. If no majority is possible, the system simply stops. Since it's a fly-by-wire system, this is catastrophic, but at least no one has to make the sorts of decisions you describe. Due to cost, the end design was for four synchronised computers, but a fifth was also carried with more limited software. This could bring the shuttle down even if the main system failed. Some flights even went out with six computers -- two that could be used as stand-alone backups to get the craft down and the main synchronised four. This limited flight backup system was indeed developed by a separate team (Rockwell won the contract) from the IBM team that developed the rest (from specs generated by Rockwell, as it happens). It's not clear if this was deliberate or simply how the contracts ended up being awarded. Maybe IBM or Rockwell could have won both and the same team that developed one system would them have written the other. I don't know. I've heard is said that four were used because that is the minimum number that can solve the Byzantine Generals Problem[1] -- synchronised action in the face of unreliable autonomous agents -- but that's not the case. The main computers simply used majority voting between three, switching the fourth in (manually!) when one of the three fails. [1] If you fancy fun read (for some value of fun) you could do worse than this which is one of my favourite papers: Lamport, Shostak, and Pease, "The Byzantine Generals Problem" ACM Transactions on Programming Languages and Systems, Vol. 4, No. 3, July 1982. -- Ben.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Continue with learning C Alla _ <modelling.data@gmail.com> - 2016-09-15 05:11 -0700
Re: Continue with learning C "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-15 05:29 -0700
Re: Continue with learning C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-15 15:01 +0100
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-15 15:32 +0100
Re: Continue with learning C Alla _ <modelling.data@gmail.com> - 2016-09-15 08:10 -0700
Re: Continue with learning C luser droog <luser.droog@gmail.com> - 2016-09-15 12:06 -0700
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-15 21:38 +0100
Re: Continue with learning C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-16 21:02 -0700
Re: Continue with learning C "Osmium" <r124c4u102@comcast.net> - 2016-09-17 08:03 -0500
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-17 22:38 +0100
Re: Continue with learning C "James R. Kuyper" <jameskuyper@verizon.net> - 2016-09-17 18:14 -0400
Re: Continue with learning C raltbos@xs4all.nl (Richard Bos) - 2016-09-18 10:47 +0000
Re: Continue with learning C Alla _ <modelling.data@gmail.com> - 2016-09-19 01:25 -0700
Re: Continue with learning C Ian Collins <ian-news@hotmail.com> - 2016-09-19 20:51 +1200
Re: Continue with learning C James Kuyper <jameskuyper@verizon.net> - 2016-09-19 09:49 -0400
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-19 15:15 +0100
Re: Continue with learning C Keith Thompson <kst-u@mib.org> - 2016-09-19 11:39 -0700
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 09:55 +0800
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-20 08:50 +0200
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 18:04 +0800
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-20 13:25 +0200
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 20:18 +0800
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-20 15:25 +0200
Re: Continue with learning C Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-20 08:45 -0400
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 22:05 +0800
Re: Continue with learning C Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-20 10:56 -0400
Re: Continue with learning C Rosario19 <Ros@invalid.invalid> - 2016-09-19 18:55 +0200
Re: Continue with learning C Anton Shepelev <anton.txt@gmail.com> - 2016-09-25 01:08 +0300
Re: Continue with learning C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-17 17:08 -0700
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-18 01:11 +0100
Re: Continue with learning C Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-17 21:32 -0400
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-18 16:27 +0200
Re: Continue with learning C Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-18 16:08 -0400
Re: Continue with learning C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-18 07:30 -0700
Re: Continue with learning C Jerry Stuckle <jstucklex@attglobal.net> - 2016-09-18 16:07 -0400
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-18 16:38 +0200
Re: Continue with learning C BartC <bc@freeuk.com> - 2016-09-18 16:37 +0100
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-18 23:54 +0800
Re: Continue with learning C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-18 16:56 -0700
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-18 17:05 +0100
Re: Continue with learning C "James R. Kuyper" <jameskuyper@verizon.net> - 2016-09-18 12:28 -0400
Re: Continue with learning C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-18 17:00 -0700
Re: Continue with learning C Alla _ <modelling.data@gmail.com> - 2016-09-19 01:40 -0700
Re: Continue with learning C "Osmium" <r124c4u102@comcast.net> - 2016-09-19 08:55 -0500
Re: Continue with learning C "Osmium" <r124c4u102@comcast.net> - 2016-09-18 11:31 -0500
Re: Continue with learning C Ian Collins <ian-news@hotmail.com> - 2016-09-19 07:25 +1200
Re: Continue with learning C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-18 20:36 +0100
Re: Continue with learning C "James R. Kuyper" <jameskuyper@verizon.net> - 2016-09-18 15:45 -0400
Re: Continue with learning C Rosario19 <Ros@invalid.invalid> - 2016-09-19 18:58 +0200
Re: Continue with learning C "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-18 09:55 -0700
Re: Continue with learning C "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-09-18 10:12 -0700
Re: Continue with learning C luser droog <luser.droog@gmail.com> - 2016-09-18 13:11 -0700
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-18 21:54 +0200
Re: Continue with learning C supercat@casperkitty.com - 2016-09-18 15:58 -0700
Re: Continue with learning C Richard Heathfield <rjh@cpax.org.uk> - 2016-09-19 07:09 +0100
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-19 10:04 +0200
Re: Continue with learning C BartC <bc@freeuk.com> - 2016-09-19 10:38 +0100
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-19 13:29 +0200
Re: Continue with learning C supercat@casperkitty.com - 2016-09-19 08:04 -0700
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 09:33 +0800
Re: Continue with learning C supercat@casperkitty.com - 2016-09-19 20:47 -0700
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-20 09:00 +0200
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-20 17:59 +0800
Re: Continue with learning C Ike Naar <ike@iceland.freeshell.org> - 2016-09-20 17:24 +0000
Re: Continue with learning C David Brown <david.brown@hesbynett.no> - 2016-09-20 08:57 +0200
Re: Continue with learning C supercat@casperkitty.com - 2016-09-20 10:53 -0700
Re: Continue with learning C Reinhardt Behm <rbehm@hushmail.com> - 2016-09-19 13:19 +0800
Re: Continue with learning C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-19 01:30 +0100
Re: Continue with learning C Alla _ <modelling.data@gmail.com> - 2016-09-19 01:15 -0700
Re: Continue with learning C Barry Schwarz <schwarzb@dqel.com> - 2016-09-15 12:38 -0700
Re: Continue with learning C fir <profesor.fir@gmail.com> - 2016-09-21 11:42 -0700
Re: Continue with learning C fir <profesor.fir@gmail.com> - 2016-09-21 12:40 -0700
Re: Continue with learning C fir <profesor.fir@gmail.com> - 2016-09-21 12:49 -0700
Re: Continue with learning C fir <profesor.fir@gmail.com> - 2016-09-23 14:47 -0700
Re: Continue with learning C fir <profesor.fir@gmail.com> - 2016-09-23 14:59 -0700
csiph-web