What is a Control Unit? Know the Definition of Control Unit

by Kelvin
What is a Control Unit?  Know the Definition of Control Unit

The Control Unit is the part of the Central Processing Unit (CPU) that controls the flow of information between memory, Arithmetic Logic Unit (ALU), and various other components in a computer. Control Unit can also be interpreted as the brain of the CPU that ensures everything works according to the instructions given.

Inside the Control Unit, there are a number of elements that allow it to perform its functions properly, for example, such as program counters, address registers, and registers that contain and read (decoding) opcodes (short for operation code which is also called instruction code or opstring). For the latter two registers, they are often referred to as a single unit by the term “instruction register”.

The program counter is a register that stores the address of the next instruction to be executed. After an instruction has been processed, the program counter will be checked again to retrieve and execute the next instruction.


It is through the information provided by the program counter that all instructions can be executed in their order. Overall, the process of retrieval to execution of this instruction is referred to as the “instruction cycle”.

Know What is a Control Unit

Instruction registers are registers used to store and read instructions through the decoding process. After decoding is complete, the control unit will issue control signals to give directions to the related components in the CPU according to the instructions that have been decoded.

Control Unit Function

1. To retrieve instructions to be processed
2. To interpret instructions which are then converted into control signals.
3. Delivering instructions that have gone through the decoding process to the ALU arithmetic and logic unit if the instructions require calculation operations or logical comparisons.
4. Sending and storing the results of executing instructions into RAM for access by the user.

Control Unit Type

To execute instructions fetched from main memory, the Control Unit must issue control signals in the correct order to avoid errors in executing the instructions. There are two approaches that can be used to generate these control signals.

Hardwired Control Unit

Know What is a Control Unit

This control unit uses a hardware-based approach to generate control signals, namely through a circuit consisting of a counter, decoder, and a number of logic gates. This approach is faster and more power efficient than microprogrammed control units, but has less flexibility.

Microprogrammed Control Unit

In this control unit, control signals are generated through programming. Programs that translate instructions and generate control signals are called microprograms, and these microprograms are stored in special memory units called control stores or control memory.

Microprogrammed Control Units have a lower speed than hardwired models because they have to process instructions that are in the control store, but are more flexible so that it is easier to execute more complicated instructions.