IBM System/360 Model 20: Difference between revisions

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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 arithmetic]].<ref name=FuncChar>{{cite book|publisher=IBM|id=A26-5847-3|title=IBM System/360 Model 20 Functional Characteristics|date=1967|url=http://www.bitsavers.org/pdf/ibm/360/functional_characteristics/A26-5847-3_360-20_funChar_Apr67.pdf}}</ref> In later years it would have been classified as a 16-bit [[minicomputer]] rather than a [[Mainframe computer|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, thatwhich allows for addition, subtraction, product, and dividend of up to 31 decimal digits.

Developed by IBM in [[Böblingen]], Germany,<ref name=Pugh>{{cite book|last1=Pugh|first1=Emerson W.|last2=Johnson|first2=Lyle R.|last3=Palmer|first3=John H.|title=IBM's 360 and Early 370 Systems|year=1991|publisher=MIT Press|isbn=0-262-16123-0|url=https://archive.org/details/ibms360early370s0000pugh|url-access=registration}}</ref>{{rp|pp.217–218,352}} the system was intended for [[Computer data processing|data processing]] and as a replacement for [[Unit record equipment|tabulating equipment]]. An incompatible small computer, the [[IBM 1130]] introduced the following year, was designed for scientific and engineering computing.

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==Remaining machines==

Despite having been sold or leased in very large numbers for a [[mainframe computer|mainframe]] system of its era, only a few of System/360 Model 20 computers remain. These are primarily the property of museums or collectors. Examples of existing systems include:

* Two Model 20 processors along with numerous peripherals (forming at least one complete system) located in Nürnberg, Germany were purchased on [[eBay]] in April/May 2019 for €3710 by two UK enthusiasts who, over the course of some months, moved the machine to [[Creslow Park]] in [[Buckinghamshire]], United Kingdom. The system was in a small, abandoned building left untouched for decades, and apparently had been used in that building since all peripherals were still fully wired and interconnected.<ref name="ibms360">{{cite web|url=https://ibms360.co.uk/?page_id=22|title=Project History|website=IBM 360 Model 20 Rescue & Restoration|access-date=2019-05-20|year=2019}}</ref> As of September 2024 the systems have been moved on a long-term loan basis to the [[System Source Computer Museum]] in [[Hunt Valley, Maryland]], USA for display and restoration.<ref>{{cite web|title=The 360’s have a new home!|work=IBM 360 Model 20 Rescue & Restoration Blog|date=September 11, 2024|url = https://www.ibm360.co.uk/?p=916}}</ref>