494 Part 5 The PMS level Section 4 Network computers and computer networks
Fig. 6. Central processor operating registers.
To sum up the characteristics of the central processor, remember that the broadbrush description is "concurrent operation." In other words, any program operating within the central processor utilizes some of the available concurrency. The program need not be written in a particular way, although centainly some optimization can be done. The specific method of accomplishing this concurrency involves issuing as many instructions as possible while handling most of the conflicts during execution. Some of the essential requirements for such a scheme include:
1 Many functional units
2 Units with three address properties
3 Many transient registers with many trunks to and from the units
4 A simple and efficient instruction set
Construction
Circuits in the 6600 computing system use all-transistor logic (Fig. 7). The silicon transistor operates in saturation when switched "on" and averages about five nanoseconds of stage delay. Logic circuits are constructed in a cordwood plug-in module of about 21/2 inches by 21/2 inches by 0.8 inch. An average of about 50 transistors are contained in these modules.
Memory circuits are constructed in a plug-in module of about six inches by six inches by 212 inches (Fig. 8). Each memory module contains a coincident current memory of 4096 12-bit words. All read-write drive circuits and bit drive circuits plus address translation are contained in the module. One such module is used for each peripheral processor, and five modules make up one bank of central memory.
Logic modules and memory modules are held in upright hinged chassis in an X shaped cabinet (Fig. 9). Interconnections between modules on the chassis are made with twisted pair transmission