The IAS operates by repetitively performing an instruction cycle. Each instruction cycle consists of two sub cycles. During a fetch cycle, the opcode of the next instruction is loaded into the IR and the address portion is loaded into MAR. This instruction may be taken from the IBR, or it can be obtained from memory by loading a word int he MBR, and then down to the IBR, IR, and MAR.
Now here, is there part I do not understand:
Why the indirection? These operations are controlled by electronic circuitry and result in the use of data paths. To simplify the electronics, there is only register that is used to specify the address in memory for a read or write and only one register used for the source or destination.
Can anyone explain this to me more intuitively? Why is this indirection being used?