ELEMENTS OF CPU:

The CPU is a complex IC chip having millions of transistors. As mentioned earlier, a CPU has three major identifiable parts: Control Unit (CU), Arithmetic & logic Unit (ALU) and a set of Registers. The CPU chip is interfaced with other components of the computer through a system bus (printed wires on the mother board) which has three sets  of wires forming Control Bus, Data Bus and Address Bus.  Figure presents the components of a CPU :  

CPU has a set of Registers which is used to store some data temporarily. Register lies above Cache and Main memory in memory hierarchy of the system. The registers in CPU perform two roles: 

• User-visible registers: used to store temporary data items and other user accessible information useful for machine or assembly language programmers. 
• Control & Status Registers: used by control unit to control and coordinate the operation of the processor.