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The generic name for the CPUs and architecture released by IBM on 1964-04-07. The 360 was marketed as a general purpose computer with 'all round' functionality - hence 360 (degrees).

Models ranged from the 360/20 to the 360/65 and later the 360/95, with typical memory configurations from 16K to 1024K.

Elements of the architecture, such as the basic instruction set are still in use on IBM mainframes today. Operating System/360 (OS/360) was developed for System/360. Other associated operating systems included DOS, OS/MFT and OS/MVT.

The 360 architecture was based on an 8-bit byte, 16 general purpose registers, 24-bit addressing, and a PSW (Program Status Word) including a location counter.

Gene Amdahl, then an IBM employee, is generally acknowledged as the 360's chief architect. He later went on to found Amdahl Corporaton, a manufacture of PCM mainframe equipment.

The 360's predecessors were the smaller IBM 1401 and the large IBM 7090 series. If was followed by the IBM 370.

See also ABEND, ALC, BAL, Big Red Switch, HCF, mode bit, PL360, PL/S.


IBM's first family of computer systems introduced in 1964. It was the first time in history that a complete line of computers was announced at one time. Although considerable enhancements have been made, much of the 360 architecture is still carried over in current-day IBM mainframes. Since its inception, trillions of dollars worth of information systems have been developed for this platform.

The 360, which took four years to develop and cost USD $5 billion ($38 billion in 2015 dollars) was a risky undertaking. Thomas Watson, Jr. literally "bet his company" on the project. The 360 has been ranked as one of the major business accomplishments in American history alongside Ford's Model T and Boeing's 707. See System/370, System/390 and IBM mainframes.

The System/360 was a bold move for IBM, because it was the first time in history a family of computers was developed and introduced. (Image courtesy of The Computer History Museum,