IBM System/360

The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It 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 binary, 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. 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. High-performance models came later. The 1967 IBM System/360 Model 91 could execute up to 16.6 million instructions per second. The larger 360 models could have up to 8 MB of main memory, 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. System/360's chief architect was Gene Amdahl, and the project was managed by Fred Brooks, responsible to Chairman Thomas J. Watson Jr. 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.