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| Manufacturer | International Business Machines Corporation (IBM) |
|---|---|
| Product family | System/360 |
| Release date | November 1964 |
| Memory | 4–32 KB Core |
The IBM System/360 Model 20 is the smallest member of the IBM System/360 family announced in November 1964. The Model 20 supports only a subset of the System/360 instruction set, with binary numbers limited to 16 bits and no floating point.[1] In later years it would have been classified as a 16-bit minicomputer rather than a mainframe, but the term "minicomputer" was not current, and in any case IBM wanted to emphasize the compatibility of the Model 20 rather than its differences from the rest of the System/360 line. It does, however, have the full System/360 decimal instruction set, that allows for addition, subtraction, product, and dividend of up to 31 decimal digits.
Developed by IBM in Böblingen, Germany,[2]: pp.217–218, 352 the system was intended for data processing and as a replacement for tab equipment. An incompatible small computer, the IBM 1130 introduced the following year, was designed for scientific and engineering computing.
The design of the Model 20 was the result of a tug of war within IBM. John Haanstra had wanted a low-end machine that could execute IBM 1401 instructions. Fred Brooks wanted the machine to have System/360 architecture. The final result was a compromise where cost concerns predominated: the system leased for under $2000 per month (equivalent to $19,648 in 2023) including Multi-Function Card Machine and line printer, compared to around $3000 (equivalent to $29,472 in 2023) for a comparable 1401.[2]: p.446
Based on number of systems sold the Model 20 was the most successful model of System/360. According to Pugh "The number of Model 20 processors installed by the end of 1970 in the United States exceeded 7,400."[2]: p.639 Other models, however, brought in greater revenue. Despite their popularity there are relatively few Model 20s in existence in working condition in 2020.[3]
- ^ IBM System/360 Model 20 Functional Characteristics (PDF). IBM. 1967. A26-5847-3.
- ^ a b c Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and Early 370 Systems. MIT Press. ISBN 0-262-16123-0.
- ^ Bradley, Adam; Blackburn, Christopher; Vaughan, Peter. "IBM 360 Model 20 Rescue and Restoration". Retrieved Mar 2, 2020.