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Early computers had many different word sizes. If you look at the 1955 Ballistic Research Laboratory document, A survey of domestic electronic digital computing

by kps 4y ago

Early computers had many different word sizes. If you look at the 1955 Ballistic Research Laboratory document, A survey of domestic electronic digital computing systems, you find lengths from a low of 10 bits to a high of 42 decimal digits. (pp234-235; Text: http://ed-thelen.org/comp-hist/BRL.html http://ed-thelen.org/comp-hist/BRL.html Scan: https://babel.hathitrust.org/cgi/pt?id=wu.89037555299&view=1up&seq=234 https://babel.hathitrust.org/cgi/pt?id=wu.89037555299&view=1... ) The influential machine to look at here, then, would be the IBM 701. Edit: The IBM 701 patent <https://patents.google.com/patent/US3197624A https://patents.google.com/patent/US3197624A> says, “A binary number of a full word of 36 bits has a precision equal to that of about a 10 decimal digit number”. It doesn't mention characters, and the machine was designed for scientific (military) calculations, not text/data processing. The associated IBM 716 printer did not use a 6-bit code. However, this does not rule out a 6-bit character code as a design consideration, even if this machine didn't use one, since IBM did have a large business in pre-computer data processing, using punched-card character sets that would fit in no less than 6 bits. So that may have driven the design of shared peripherals like 7-track tape (6 bits plus parity) and led to a multiple-of-6 word size. Edit 2: The paper, The logical organization of the new IBM scientific calculator <https://doi.org/10.1145/609784.609791 https://doi.org/10.1145/609784.609791> again mentions 10 decimal digits. It also describes card and printer I/O, and it is explicit that these work on binary card images, row by row, not character by character. The machine handles only 72 columns of an 80-column card, reading a row at a time into two 36-bit words. A 40-bit word would have let it use the whole card!

kps 4y ago
From Stephen H. Kaisler, First Generation Mainframes: The IBM 700 Series: > IBM conducted a survey of existing machines and applications, ultimately determining that a word length of between 10 and 12 digits or about 35 to 41 bits was desirable. Additionally, single address machines required at least 18 bits for storage of operation codes and addresses given a specified memory size. Since the secondary memory was magnetic tape, a tape technology study showed that 6 parallel channels for data storage were optimal. Thus, the word size should be a multiple of 6 bits so that subparts of the word could be stored in successive locations on tape. As a result, IBM arrived at 36 bits for the IBM 701 word size. https://books.google.ca/books?id=B9l9DwAAQBAJ&lpg=PR4&pg=PA5#v=onepage&q&f=false https://books.google.ca/books?id=B9l9DwAAQBAJ&lpg=PR4&pg=PA5...
- kps 4y ago
  From Herb Grosch, Computer: Bit Slices of a Life: > The 36-bit word size was probably unfortunate, and it most certainly stretched the abilities of customer problem analysts and programming experts later. When you chopped off a piece for the exponent (and sign) in floating point - which in spite of my Jeremiads all the customers except maybe the cryptologists insisted on using - there wasn't really enough left for accurate matrix calculations. Or astronomy, but I could already see before the design was fully roughed out that not much of Wallace's stuff was ever going to run on a Defense Calculator! Anyhow, it was too late; looking back from the Eighties, I guessed 48 bits would have been optimal; the 360/370 experience showed us that 32 is not enough, and 64 would have been wasteful. http://www.columbia.edu/cu/computinghistory/computer.html http://www.columbia.edu/cu/computinghistory/computer.html
  - DougMerritt 4y ago
    That's a lot of great material. Thanks!

by kps 4y ago

kps 4y ago

From Stephen H. Kaisler, First Generation Mainframes: The IBM 700 Series: > IBM conducted a survey of existing machines and applications, ultimately determining that a word length of between 10 and 12 digits or about 35 to 41 bits was desirable. Additionally, single address machines required at least 18 bits for storage of operation codes and addresses given a specified memory size. Since the secondary memory was magnetic tape, a tape technology study showed that 6 parallel channels for data storage were optimal. Thus, the word size should be a multiple of 6 bits so that subparts of the word could be stored in successive locations on tape. As a result, IBM arrived at 36 bits for the IBM 701 word size. https://books.google.ca/books?id=B9l9DwAAQBAJ&lpg=PR4&pg=PA5#v=onepage&q&f=false https://books.google.ca/books?id=B9l9DwAAQBAJ&lpg=PR4&pg=PA5...

kps 4y ago
From Herb Grosch, Computer: Bit Slices of a Life: > The 36-bit word size was probably unfortunate, and it most certainly stretched the abilities of customer problem analysts and programming experts later. When you chopped off a piece for the exponent (and sign) in floating point - which in spite of my Jeremiads all the customers except maybe the cryptologists insisted on using - there wasn't really enough left for accurate matrix calculations. Or astronomy, but I could already see before the design was fully roughed out that not much of Wallace's stuff was ever going to run on a Defense Calculator! Anyhow, it was too late; looking back from the Eighties, I guessed 48 bits would have been optimal; the 360/370 experience showed us that 32 is not enough, and 64 would have been wasteful. http://www.columbia.edu/cu/computinghistory/computer.html http://www.columbia.edu/cu/computinghistory/computer.html
- DougMerritt 4y ago
  That's a lot of great material. Thanks!