Section 5
The System/360 and System/370 Family
The System/360 was the first planned computer family to cover a range of cost and performance. The System/360 predecessors, the IBM 7090 series and the business models, ran into a number of the same problems of limited growth potential later encountered by the PDP-8. Rather than continuing to tinker with the architecture, IBM opted for a totally new ISP planned right from the start to have growth potential for the future covering both the scientific and business market. Even the initial family plan called for a wide range of cost and performance implementations. Microcode was also extensively used to provide emulation support for prior IBM systems.
Subsequently the System/360 ISP evolved into the System/370. Chapter 51 describes the problems with developing an upward-compatible ISP extension.
Within one generation of technology, the System/360 and System/370 used various implementation techniques (e. g., wider data paths and processor-memory overlap) to provide a performance range. But in the System/370 series, several models have been reimplemented for constant cost and increased performance. The 3030 series and, in 1979, the 4300 series were introduced as lower-cost, constant-performance models of the System/370 ISP. Chapter 52 discusses and analyzes the various family members.
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