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From Stephen H. Kaisler, First Generation Mainframes: The IBM 700 Series: > IBM conducted a survey of existing machines and applications, ultimately

by 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 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!