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What pushed computing toward eight bit bytes is the IBM System/360 (1964) which dominated the computing industry at the time. It used 8-bit EBCDIC (with ASCII a

by kens 4y ago

What pushed computing toward eight bit bytes is the IBM System/360 (1964) which dominated the computing industry at the time. It used 8-bit EBCDIC (with ASCII as an afterthought). If ASCII didn't exist, we'd still be using byte-based systems and hexadecimal. Prior to System/360, business data processing typically used 6-bit characters (e.g. IBM 1401), which only gave you upper case. Scientific processing used whatever word size gave the desired accuracy, so it was totally reasonable to have a 15-bit computer or a 26-bit computer. Powers of two for the word size are convenient for slicing up words into smaller pieces and for specifying a bit in the word. But you also have systems like the Four Phase, which used 24-bit words consisting of 3 bytes. (Which turned out to be a mess when you try to extract bytes from words.)

jameshart 4y ago
But you only care about the difficulty of extracting eight-bit bytes from words because you need to do things like interoperate with protocols or storage media based on eight bit bytes, or eight bit parallel interfaces. If everything were based on a different basic ‘byte’ size that objection would go away. Sure, oddball things that used 8-bit data would exist and you’d need to work with them - but in our 8-bit world oddball things based on 10-bit protocols exist and we live with the impedance mismatches that causes.
- Dylan16807 4y ago
  But what other byte sizes are viable? 6 bits isn't enough. 7 bits is viable for characters but at that point there's strong pressure to move up to 8 as a power of two. 9 fits neatly into octal but there's little advantage over 8 so you're probably going to prefer either 8 or 10. Between 8 and 10, I could see 10 winning. But either way octal isn't doing very hot.
  - lokedhs 4y ago
    36 bits is very neat, and used by several machines including the PDP-10. The smallest unit doesn't have to be a single character.

by kens 4y ago

jameshart 4y ago

But you only care about the difficulty of extracting eight-bit bytes from words because you need to do things like interoperate with protocols or storage media based on eight bit bytes, or eight bit parallel interfaces. If everything were based on a different basic ‘byte’ size that objection would go away. Sure, oddball things that used 8-bit data would exist and you’d need to work with them - but in our 8-bit world oddball things based on 10-bit protocols exist and we live with the impedance mismatches that causes.

Dylan16807 4y ago
But what other byte sizes are viable? 6 bits isn't enough. 7 bits is viable for characters but at that point there's strong pressure to move up to 8 as a power of two. 9 fits neatly into octal but there's little advantage over 8 so you're probably going to prefer either 8 or 10. Between 8 and 10, I could see 10 winning. But either way octal isn't doing very hot.
- lokedhs 4y ago
  36 bits is very neat, and used by several machines including the PDP-10. The smallest unit doesn't have to be a single character.