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Chapter 43 The structure of SYSTEM/360 589

Fig. 1. Functional schematic of System/360.

vided: logical manipulation of individual bits, character strings and fixed words; decimal arithmetic on digit strings; fixed-point binary arithmetic; and floating-point arithmetic. The processing unit, together with the central control function, will be referred to as the central processing unit (CPU). The basic registers and data paths of the CPU are shown in Fig. 2.

The CPU's of the various models yield a substantial range in performance. Relative to the smallest model (Model 30), the internal performance of the largest (Model 70) is approximately 50:1 for scientific computation and 15:1 for commercial data processing.


Because of the extensive instruction set, SYSTEM/360 control is more elaborate than in conventional computers. Control functions include internal sequencing of each operation; sequencing from instruction to instruction (with branching and interruption); governing of many I/O transfers; and the monitoring, signaling, timing, and storage protection essential to total system operation. The control equipment is combined with a programmed supervisor, which coordinates and issues all I/O instructions, handles excep-

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