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IBM 360

System/360
Designer IBM
Bits 32-bit
Introduced 1964; 53 years ago (1964)
Design CISC
Type Register-Register
Register-Memory
Memory-Memory
Encoding Variable (2, 4 or 6 bytes long)
Branching Condition code, indexing, counting
Endianness Big
Page size N/A, except for 360/67
Open Yes
Registers
General purpose 16× 32-bit
Floating point 4× 64-bit

The IBM System/360 (S/360) is a mainframe computer system family 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 the complete range of applications, from small to large, both commercial and scientific. The design made a clear distinction between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the incompatible model 44 and the most expensive systems used microcode to implement the instruction set, which featured 8-bit byte addressing and binary, decimal and (hexadecimal) floating-point calculations.

The launch of the System/360 family introduced IBM's Solid Logic Technology (SLT), a new technology that was the start of 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 do up to 16.6 million instructions per second. The larger 360 models could have up to 8 MB of main memory, though main memory that big was unusual—a more typical 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.

The IBM 360 was extremely successful in the market, allowing customers to purchase a smaller system with the knowledge they would always be able to migrate upward if their needs grew, without reprogramming of application software or replacing peripheral devices. Many consider the design one of the most successful computers in history, influencing computer design for years to come.


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