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→incorrect use of term bytecode: 1 to 56 byte instructions! |
Guy Harris (talk | contribs) →First sentence is wrong: Microcoded machines are often not just "SIMH in control store"-type machines; they may even have significant assistance from specialized hardware. S/360's instruction set didn't look like bytecode; it wasn't even byte-aligned, it was halfword-aligned. |
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::But okay, MIX. MIX is designed to be either binary or decimal, such that properly written programs run in either case. Assuming ''byte'' means eight-bit unit, I think that disqualifies MIX. But the idea isn't so far off. Back to the years close to the beginning of MIX, decimal machines were not so rare for commercial processors. I suspect, though, that Knuth was trying to get people to think more generally. [[User:Gah4|Gah4]] ([[User talk:Gah4|talk]]) 18:47, 11 August 2025 (UTC)
:::The [[IBM 7030]] used 64-bit words. Other vendors had 48-bit and 60-bit scientific machines. The wierdest was the [[UNIVAC LARC]], which had a 12-digit word but allowed \ (ignore), ^ (space), - (minus), . (period) and + (plus) as digits. -- [[User:Chatul|Shmuel (Seymour J.) Metz Username:Chatul]] ([[User talk:Chatul|talk]]) 10:52, 12 August 2025 (UTC)
:::{{tq| Bytecode should apply to any byte oriented instruction encoding, back to (as far as I know) IBM System/360.}} S/360 is a byte-addressable processor, but its ''instruction set'' isn't byte-aligned, it's halfword-aligned.
:::{{tq|An important idea behind S/360 was the low-end microcoded machines. That is, ones that interpret the instructions in software.}} Microcoding goes anywhere from "it's kinda like [[SIMH]]" vertical microcode, where it looks like a software interpreter, to "it's a state machine defined by words in a control memory with bitfields that either go directly to CPU circuit or control which next control memory word is fetched" horizontal microcode, with various types in between. Often instruction fetch and decode is helped by specialized hardware controlled by the microcode, or is done by a separate hardwired or microcoded engine, with the results fed to a separate execution unit. [[User:Guy Harris|Guy Harris]] ([[User talk:Guy Harris|talk]]) 23:30, 14 August 2025 (UTC)
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