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Chapter 52

The IBM System/360, System/370, 3030, and 4300: A Series of Planned Machines That Span a Wide Performance Range

C. G. Bell / A. Newell / M. Reich / D. Siewiorek


In this section, besides making some general comments on the IBM System/36O and System/370 series and System/370 follow-ons, we will attempt an analysis of the performance and costs of the series. Performance is notoriously difficult to measure, as we noted in Chap. 5, and costs are even more so. With respect to the latter, what is publicly available is price data, not manufacturing cost data.

These prices reflect not only marketing policies but also accounting policies within the organization for the attribution of cost to product lines. Nevertheless, the 360 and 370 series provide two things which make a comparative analysis worthwhile. First, the common ISP makes simple performance measures more comparable; second, the common manufacturer makes relative prices more a reflection of relative costs than would otherwise he the case. Neither of these aspects is perfect, as we will note at several points in the discussion. Nevertheless, the 360 and 370 series provide as good an opportunity to attempt cost/performance analysis as we know.

Analyses of the type we attempt here produce only rather crude pictures and are subject to question if all the input data are not very carefully checked. We have not done this, depending instead on published sources. For the purpose of this book, illustration of the style of analysis seems sufficient. In addition, using a performance measure based only on Pc power measurements leaves many questions unanswered because it does not address the soft areas of analysis relating to throughput, task environment, and the operating-system software.

Figure 1 depicts the family tree of IBM computers as a function of introduction date and relative processing power. It can be used as a concise summary and reference for the following discussions. The reader is encouraged to follow the procession of this chapter on Fig. 1.

The IBM System/360 architecture was introduced in Chap. 40. The series has been superseded by the IBM System/370, 3030, and 4300 series. Each series is upward-compatible with the System/360 so far as the user problem state is concerned. The series also share an upward-compatible ISP, as outlined in Chap. 51. The various models differ in interpreter speeds and PMS structure. Many PMS elements are used in common, particularly K's, Ms's, and T's. The 3030 and 4300 series constitutes the currant primary IBM product line.

The System/360, System/370, 3030, and 4300 series are presented both because IBM's market dominance makes it the most prevalent mainframe computer and because its implementations span the largest performance and price range of any series. The various models are compared in Table 1.

This chapter will open with a discussion of the various 360, 370, 3030, and 4300 series models. Finally, the System/360-System/370 series will be evaluated in terms of cost and performance.

The IBM System/360 Family

Figure 2 illustrates the introduction dates of the various System/360 models. Chapters 40, 41, and 12 discuss the logical structure of the System/360, the implementations,1 and the microprogrammed Model 30, respectively.

A succinct description of the design goals and innovations is given in the abstract of Amdahl, Blaauw, and Brooks [1964]. The architecture2 of the newly accounted IBM System/360 featured four innovations:

1 An approach to storage which permits and exploits very large capacities, hierarchies of speeds, read-only storage for microprogram control, flexible storage protection, and simple program relocation.

2 An input/output system offering new degrees of concurrent operation; compatible channel operation; data rates approaching 5 million characters per second; integrated design of hardware and software; a new, low-cost, multiple-channel package sharing mainframe hardware; new provisions for device status information; and a standard channel interface between central processing unit and input/output devices.

3 A truly general-purpose machine organization offering new supervisory facilities, powerful logical processing operations, and a wide variety of data formats.

4 Strict upward and downward machine language compatibil

1Chapters 40 and 41 are from IBM Systems Journal, vol. 3, no. 2, 1964, which was devoted exclusively to the System/360. Other articles, listed in the bibliography at the end of this chapter, are recommended for additional details.

2The term architecture is used here to describe the attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation.


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