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Section 3 The IBM System/360-a series of planned machines which span a wide performance range 587

5 between a 4 x 1 power processor and 20 power processor. The largest gap in the System/360 is a factor of 3 between Models 30 and 40.


The IBM System/360, by achieving a production record, has fulfilled its principal design objective. The technical goals, however, are of interest to us here. The most interesting aspect of the design is achieving a performance range of 314 to 1 over a series of models, with a primary-memory size range of 2,048 to 1 for various computer configurations. Thus a user is given a very large set of configuration alternatives. The SLT technology, though not integrated-circuit, is certainly of the third generation. Using SLT the fabrication of the models is superb.

There is a vast array of secondary-memory and terminal devices to couple with almost any other system. The System/360 is the first computer to make extensive use of microprogramming. Microprogramming is used for the definition of the System/360 instruction-set processor, but, more important, microprograms define previous IBM computers so that a user can operate satisfactorily during the interim period when older programs are being updated to use the System/360. There are provisions for multicomputer structures. Within a single computer structure there is adequate means of peripheral switching so that reliable and high-performance structures can be assembled. Early structures do not provide multiprocessing; we have suggested multiprocessing as a technique to achieve the same performance-range objectives. The io processor, though rather elaborate, provides a certain commonality.

The instruction-set processor for the System/360, based on a general-registers structure, appears to be overly complex, yet incomplete, because there are so many data types. The addressing mechanism and lack of multiprogramming ability make the System/360 a hard machine to appreciate fully. Although we praise microprogramming as a means of accomplishing compatibility with the past, it appears to stand in the way of getting the most performance from the hardware. Perhaps of most significance, the System/360 may have a greater lifetime than any past computer.

Selected Bibliography

Architecture and logical structure: AmdaG64a (TeagH65)1, BlaaG64a2, BlaaG64b2 General implementations: AmdaG64b2, CartW64, PadeA642, StevW642 Microprogramming: GreeJ64, TuckS67, WebeH67; Formal description of Pc5 FalkA642 Performance and reviews: HillJ66, SoloM66; Model 40 modifications for multiprogramming: LindA66; Model 67: ArdeB66, FikeR68, GibsC66, LaueH67; Model 85: ContC683, LiptJ683, PadeA683 Model 91 architecture and technology: AndeD674, AndeS674, BolaL674, FlynM674a, LangJ673, LloyR674, SechR674, TomaR674 Model 92 (proposed): ContC64 (GrimR65a), AmdaG64c (GrimR65b), ChenT64 (GrimR65c); Serviceability: CartW64; Other references: AdamC62, CorbF62, GrosH53, SharW69, WilkM65; IBM reference manuals: IBM System/360 Functional characteristics manuals for each model, IBM System/360 Configurator (diagram) for each model, A22-6821-4 IBM System/360 Principles of Operation, A22-6810-8 IBM System/360 System Summary

1 ( ) denotes the review of previous article.

2IBM Systems Journal, vol. 3, nos. 2 and 3, 1964.

3IBM Systems Journal, vol. 7, no. 1, 1968.

4IBM Journal of Research and Development, vol. 11, no. 1, January, 1967.

5Given in A Programming Language/APL [Iverson, 1962].

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