732 Part 3 ½ Computer Classes
Section 4 ½ Maxicomputers

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.
 
 

Central Processor

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 processor. These are the two increment units, floating add unit, fixed add unit, shift unit, two multiply units, divide unit, boolean unit, and branch unit. In a general way, each of these units is a three address unit. As an example, the floating add unit obtains two 60-bit operands from the central registers and produces a 60 bit result which is returned to a register. Information to and from these units is held in the central registers, of which there are twenty-four. Eight of these are considered index registers, are of 18 bits length, and one of which always contains zero. Eight are considered address registers, are of 18 bits length, and serve to address the five read central memory trunks and the two store central memory trunks. Eight are considered floating point