Learning Resources

CPU Internals

The following sections explain the internal components of the Central Processor Unit or CPU. Taken on their own they will mean very little and the explanation of their use should be read in conjunction with the explanation Fetch-Execute Cycle of the CPU.

Control Unit (CU): The control unit of the CPU does exactly what its name would suggest. Its purpose is to control all of the other elements of the CPU, ensuring that they do what they should, when they should.

Arithmetic and Logic Unit (ALU): The ALU is a part of the CPU that can carry out arithmetic operations - addition and subtraction and, depending on the processor, multiplication and division, logic operations - AND, OR, NOT, XOR and bit-shift operations - shift bits in a word either left or right. (This corresponds to multiplying or dividing by 2.)

Decoder: The decoder is a logic circuit that exists to take the binary representation of an instruction and initiate the execution of the appropriate instruction. It usually exists as part of the control unit.

Registers: Registers are small pieces of memory located inside the CPU. They can be thought of as the hardware version of a variable in software