This paper discusses the design considerations for the architectural extensions that distinguish Systeni/370 from Systeni/360. It comments on some experiences with the original objectives foi* System/360 and on the efforts to achieve them, and it describes the reasons and objectives for extending the architecture. It covers virtual storage, program control, data-manipulation instructions, timing facilities, multiprocessing, debugging and monitoring^ error handling, and input/output operations. A final section tabulates some of tbe important parameters of the vaiious IBM macbines wbich implement the architecture.

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