The control bus provides timing signals to synchronise the flow of data between the processor and memory subsystem or peripheral devices. The CPU is said to be the brains of any computer system. It provides all the timing and control signals necessary to transfer data from one point to another in the system. Instructions are held in the memory section of the computer system. Instructions are transferred one at a time into the CPU, where they are decoded then executed.
Instructions follow each other in successive memory locations.
The processor unit keeps track of the instruction it is executing by using a internal counter. This counter holds the location in memory of the instruction it is executing. Stored Program Control Most computer systems today are stored program control systems. This means that the processor executes instructions which are stored in a memory subsystem. SPC systems are popular, because the processor does is simply changed by altering the instruction in the memory system.