5 ms·

I worked on United's computer systems for a year (never that one though), and so I get nervous when I see a headline like that. True story: one of their systems

I worked on United's computer systems for a year (never that one though), and so I get nervous when I see a headline like that. True story: one of their systems still runs on a mainframe that has 9 bits in a byte!

themartorana 11y ago
I did not know that was ever a thing. I knew that bit counts had been lower - 5 or 6 - but assumed once we hit 8, the whole power-of-2 thing was too comfortable in a binary system to ever be anything besides a power of 2 again - and sure enough, we get 16 bit, 32 bit, and 64 bit systems, and double-byte and triple-byte char sets, etc. Need more space? Take another byte. Was the 9th bit special? Or just a standard bit in the byte?
- Lx1oG-AWb6h_ZG0 11y ago
  Someone probably read too much Iain M. Banks and decided to adopt Marain's base-9 system :) If I'm not mistaken, some old consoles used a 9-bit RGB encoding, so this could theoretically help there. Minecraft also uses a 9-bit system for Redstone, afaik.
- chiph 11y ago
  The PowerPC based AS/400 systems were technically 65-bit machines, as the extra bit was a privilege flag to separate system code from user code. Hardware enforced security - one reason why it is such a stable machine.
- Someone 11y ago
  36 bit was popular for scientific computing because 35 gives you a sign bit and 10 decimal digits (yes, that's weird, but that's the argument I read everywhere, including at https://en.m.wikipedia.org/wiki/36-bit https://en.m.wikipedia.org/wiki/36-bit. 35 likely was skipped because it its only divisors are 5 and 7, limiting instructions to 7 bits even then was felt to be too restricting. For some architectures, the DoD had a say in this, too. See https://en.m.wikipedia.org/wiki/Unisys_2200_Series_system_architecture https://en.m.wikipedia.org/wiki/Unisys_2200_Series_system_ar...) 36 bits got us the 6-bit character (10 digits, 26 letters, and punctuation) with six characters in a word. Because of that, some OSes had six-character file names. If you want to get upper- and lowercase, you need more than 6 bits. 9 is the smallest divisor larger than 6 of 36, so nine-bit characters made sense. On such systems, file names could still use 6-bit characters, while applications used 9-bit ones. Also, some instructions could work on words, half words, quarter words, or sixth words.
- wmf 11y ago
  If hex hadn't been invented yet, 9 bits works better with octal. I don't know if that was a factor.
temuze 11y ago
Oh god stories like this scare me. One of my friends used to intern for a very large company that maintained software for flight control towers. His entire summer was spent writing bash tests for these old Fortran apps that kept planes from running into each other. Most of the mainframes still had tape. That's the code that keeps track of our planes.
- Xylakant 11y ago
  I must admit I don't take that as a negative thing. Code that's so old had a lot of time for corner cases to be ironed out. If it's maintained properly it's probably less buggy than any rewrite, even though fortran is less enticing than rust as a language.
StillBored 11y ago
Sabre, still runs all their reservations through ztpf... If you know anyone there ask them about how they get the data off the mainframe. The story I heard sounds like the process was designed by Rube Goldberg.

themartorana 11y ago

I did not know that was ever a thing. I knew that bit counts had been lower - 5 or 6 - but assumed once we hit 8, the whole power-of-2 thing was too comfortable in a binary system to ever be anything besides a power of 2 again - and sure enough, we get 16 bit, 32 bit, and 64 bit systems, and double-byte and triple-byte char sets, etc. Need more space? Take another byte. Was the 9th bit special? Or just a standard bit in the byte?

Lx1oG-AWb6h_ZG0 11y ago
Someone probably read too much Iain M. Banks and decided to adopt Marain's base-9 system :) If I'm not mistaken, some old consoles used a 9-bit RGB encoding, so this could theoretically help there. Minecraft also uses a 9-bit system for Redstone, afaik.
chiph 11y ago
The PowerPC based AS/400 systems were technically 65-bit machines, as the extra bit was a privilege flag to separate system code from user code. Hardware enforced security - one reason why it is such a stable machine.
Someone 11y ago
36 bit was popular for scientific computing because 35 gives you a sign bit and 10 decimal digits (yes, that's weird, but that's the argument I read everywhere, including at https://en.m.wikipedia.org/wiki/36-bit https://en.m.wikipedia.org/wiki/36-bit. 35 likely was skipped because it its only divisors are 5 and 7, limiting instructions to 7 bits even then was felt to be too restricting. For some architectures, the DoD had a say in this, too. See https://en.m.wikipedia.org/wiki/Unisys_2200_Series_system_architecture https://en.m.wikipedia.org/wiki/Unisys_2200_Series_system_ar...) 36 bits got us the 6-bit character (10 digits, 26 letters, and punctuation) with six characters in a word. Because of that, some OSes had six-character file names. If you want to get upper- and lowercase, you need more than 6 bits. 9 is the smallest divisor larger than 6 of 36, so nine-bit characters made sense. On such systems, file names could still use 6-bit characters, while applications used 9-bit ones. Also, some instructions could work on words, half words, quarter words, or sixth words.
wmf 11y ago
If hex hadn't been invented yet, 9 bits works better with octal. I don't know if that was a factor.

temuze 11y ago

Oh god stories like this scare me. One of my friends used to intern for a very large company that maintained software for flight control towers. His entire summer was spent writing bash tests for these old Fortran apps that kept planes from running into each other. Most of the mainframes still had tape. That's the code that keeps track of our planes.

Xylakant 11y ago
I must admit I don't take that as a negative thing. Code that's so old had a lot of time for corner cases to be ironed out. If it's maintained properly it's probably less buggy than any rewrite, even though fortran is less enticing than rust as a language.

StillBored 11y ago

Sabre, still runs all their reservations through ztpf... If you know anyone there ask them about how they get the data off the mainframe. The story I heard sounds like the process was designed by Rube Goldberg.