Architecture

Instruction buffer register (IBR): Employed to hold temporarily the right hand instruction from a word in memory.

Program counter (PC): It contains the address of the next instruction pair to be fetched from memory.

Accumulator (AC) and multiplier quotient (MQ): Employed to hold temporarily operands and results of ALU operations. For example, the result of multiplying two 40 – bit numbers is an 80 – bit number; the most significant 40 bits are stored in the AC and the least significant in the MQ.