IBM System/360

System/360

IBM System/360 Model 30 central processor unit (CPU)
Also known as	S/360
Developer	IBM
Manufacturer	IBM
Product family	See table of models
Type	Mainframe computer
Release date	April 7, 1964; 61 years ago (1964-04-07)
Discontinued	1978; 47 years ago (1978)
Media	7-track tape 9-track tape DASDs paper tape printed paper punched cards
Operating system	BOS/360 TOS/360 DOS/360 OS/360 TSS/360
Memory	8 KB – 9 MB (core memory) (thin-film memory on the Model 95))
Predecessor	700/7000 series
Successor	System/370
Related	System/360 architecture

The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964,^[1] and delivered between 1965 and 1978.^[2] System/360 was the first family of computers designed to cover both commercial and scientific applications and a complete range of applications from small to large. The design distinguished between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible Model 44 and the most expensive systems use microcode to implement the instruction set, featuring 8-bit byte addressing and fixed-point binary, fixed-point decimal and hexadecimal floating-point calculations. The System/360 family introduced IBM's Solid Logic Technology (SLT), which packed more transistors onto a circuit card, allowing more powerful but smaller computers.^[3]

System/360's chief architect was Gene Amdahl, and the project was managed by Fred Brooks, responsible to Chairman Thomas J. Watson Jr.^[4] The commercial release was piloted by another of Watson's lieutenants, John R. Opel, who managed the launch of IBM's System 360 mainframe family in 1964.^[5] The slowest System/360 model announced in 1964, the Model 30, could perform up to 34,500 instructions per second, with memory from 8 to 64 KB.^[6] High-performance models came later. The 1967 IBM System/360 Model 91 could execute up to 16.6 million instructions per second.^[7] The larger 360 models could have up to 8 MB of main memory,^[4] though that much memory was unusual; a large installation might have as little as 256 KB of main storage, but 512 KB, 768 KB or 1024 KB was more common. Up to 8 megabytes of slower (8 microsecond) Large Capacity Storage (LCS) was also available for some models.

The IBM 360 was extremely successful, allowing customers to purchase a smaller system knowing they could expand it, if their needs grew, without reprogramming application software or replacing peripheral devices. It influenced computer design for years to come; many consider it one of history's most successful computers. Application-level compatibility (with some restrictions) for System/360 software is maintained to the present day with the System z mainframe servers.