3 ms·
> eight bit byte rather than the cheaper 7 bits being considered for the IBM 360 That's 8-bit vs. 6-bit bytes. See "Interview: An interview with Fred Brooks",
by dalke 4y ago
> eight bit byte rather than the cheaper 7 bits being considered for the IBM 360
That's 8-bit vs. 6-bit bytes. See "Interview: An interview with Fred Brooks", Communications of the ACM, Volume 58, Number 11 (2015), Pages 36-40 https://dl.acm.org/doi/fullHtml/10.1145/2822519 https://dl.acm.org/doi/fullHtml/10.1145/2822519 .
> Gene's machine was based on the existing 6-bit byte and multiples of that: 24-bit instructions and a 48-bit instruction or floating point ... Of all my technical accomplishments, making the 8-bit byte decision is far and away the most important. The reason was that it opened up the lowercase alphabet. I saw language processing as being another new market area that we were not in, and could not get into very well as long we were doing 6-bit character sets.
From your [0], "Architecture of the IBM System/360" (1964) at https://cpb-us-w2.wpmucdn.com/sites.gatech.edu/dist/8/175/files/2015/08/IBM-360.pdf https://cpb-us-w2.wpmucdn.com/sites.gatech.edu/dist/8/175/fi... see the section "Character size, 6 vs 4/8", which discusses 4/6, 6, and 8-bit codes and the reasoning for 8-bit, and which comments:
> The selection of the 8-bit character size in 1961 proved wise by 1963, when the American Standards Association adopted a 7-bit standard character code for information interchange (ASCII).
FWIW, [0] is from April 1964. He also used "computer architecture" in the earlier "Architectural Philosophy", which is chapter 2 of the 1962 book "Planning A Computer System" concerning Project Stretch, at https://archive.org/details/bitsavers_ibm7030Plam_46781927/page/n29/mode/2up https://archive.org/details/bitsavers_ibm7030Plam_46781927/p...
- pjmorris 4y agoThank you for the corrections, I learned something.
- kristianp 4y ago7 bits was enough for ASCII and lower case, why not 7?
- sedatk 4y agoI'd guess because it's not an even number. I don't know why even number of bits were considered infeasible, but there hasn't been a single computer architecture with odd number of bits as word length: https://en.wikipedia.org/wiki/Word_(computer_architecture) https://en.wikipedia.org/wiki/Word_(computer_architecture)
- versteegen 4y ago??? The table on that article contains plenty of architectures with odd bits per word, for example the Apollo Guidance Computer (15). Odd bits often resulted from sign or parity bits. And I'm shocked to see decimal digits were sometimes encoded as 5 to 7 bits to a digit (bi-quinary coded decimal) rather than 4 (binary coded decimal), e.g. in the IBM 650 (10 digits and a sign bit), which used 71 bits per word - a prime number! Of course "bit" is not the right term here, as software can't access them. But there are 71 physical switches exposed to the user for input.
- kristianp 4y agoThat might give a clue: An 8-bit word can fit two bcd digits.