Chapter 39 Parallel operation in the Control Data 6600 491

Input-output channels are bi-directional, 12-bit paths. One 12-bit word may move in one direction every major cycle, or 1000 nanoseconds, on each channel. Therefore, a maxim m burst rate of 120 million bits per second is possible using all ten peripheral processors. A sustained rate of about 50 million bits per second can be maintained in a practical operating system. Each channel may service several peripheral devices and may interface to other systems, such as satellite computers.

Peripheral and control processors access central memory through an assembly network and a dis-assembly network. Since five peripheral memory references are required to make up one central memory word, a natural assembly network of five levels is used. This allows five references to be "nested" in each network during any major cycle. The central memory is organized in independent banks with the ability to transfer central words every minor cycle. The peripheral processors, therefore, introduce at most about 2% interference at the central memory address control.

A single real time clock, continuously running, is available to all peripheral processors.

The 6600 central processor may be considered the high-speed arithmetic unit of the system (Fig. 3). Its program, operands, and results are held in the central memory. It has no connection to the peripheral processors except through memory and except for two single controls. These are the exchange jump, which starts or interrupts the central processor from a peripheral processor, and the central program address which can be monitored by a peripheral processor.

A key description of the 6600 central processor, as you will see in later discussion, is "parallel by function." This means that a number of arithmetic functions may be performed concurrently. To this end, there are ten functional units within the central