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36-Bit Word Length36-bit word length describes the number of bits, 36, used in some early computers to represent data in the form of words – the basic information units (besides the bits) in the machines. Since the mid-1960s, word lengths like 16 and 32, both being powers of two, have become the norm. Many early computers aimed at the scientific market had a 36-bit word length. This word length was just long enough to represent positive and negative numbers to an accuracy of ten decimal digits (actually 35 bits would have been the minimum). It also allowed the storage of six alphanumeric characters. Prior to the introduction of computers, the state of the art in precision scientific and engineering calculation was the ten-digit, electrically-powered, mechanical calculator, such as those manufactured by Frieden, Marchant and the Monroe Calculator Company. These calculators had a column of keys for each digit and operators were trained to use all their fingers when entering numbers, so while some specialized calculators had more columns, ten was a practical limit. Computers, as the new kid on the block, had to match that accuracy. Early computers with 36-bit words included the MIT Lincoln Laboratory TX-2, the IBM 701/704/709/7090/7040 series, the Univac 1103/1103A/1105 series and 1107/1108/1106/1110 series and the Digital Equipment Corporation PDP-6/PDP-10 series machines (as used in the DECsystem-10 and DECSYSTEM-20) also employed a 36-bit word length. Smaller machines, like the PDP-1, PDP-9 and PDP-15 used 18-bit words so a double word would be 36-bits. Decimal computers sold in that era, such as the IBM 650 and the IBM 7070, had a word length of ten digits. By the time IBM introduced System/360, scientific calculations had shifted to floating point and mechanical calculators were no longer a competitor, so the 360's practice of using word lengths that were a power of two quickly became universal.
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