Control Unit and its types.

Design of Control Unit

• The control unit retrieves instructions in the form of bit-by-bit representations from the CPU's memory and converts them into control signals, that occupy a form of light or electrical pulses. 
• The signals are instructions that other computer components must obey.
• The main memory and ALU are in communication with the control unit. 

CPU

• It also regulates the communication between the memory, the processor, and the different peripherals. 
• It also tells the ALU what action needs to be taken with the data.

Control Unit

There are two ways to create a control unit, which are listed below:

Hardwired Control Unit

Hardwired Control Unit

• Hardware components like flip flops, gates, and decoders are used to implement it. 
• The instruction register, flags, timing signals, and other signals are the inputs to the control unit. 
• If we have to make the control unit huge, this arrangement can become extremely complex.
• All combinational circuits must be modified if the design needs to be altered, which is a highly challenging task.

Some advantages of hardwired control unit

1. Hardwired Control Units are quick due to their usage of combinational circuits for signal generation.
2. The amount of delay that can occur in the creation of control signals depends on the number of gates.
3. It is capable of being tuned to generate the quick mode of operation.
4. Quicker than a control unit with microprogramming.
5. Control memory is not necessary.

Microprogrammed Control Unit

• It is put into practice through the use of programming. 
• A program made up of micro-instructions is run in order to perform a series of micro-operations. 
• Any adjustments or changes in this organization can be made by the programmer by upgrading the micro program in the control memory.

Some advantages of microprogrammed control unit

1. It enables a control unit design that is more methodical.
2. It is simpler to adjust and troubleshoot.
3. It can maintain the basic structure of the control function.
4. It may simplify the design of the control unit. It is therefore less costly and less prone to malfunctions.
5. It is capable of designing in a methodical and structured way.
6. Rather than controlling hardware-based operations, it is used to control software-based operations.
7. It is more flexible.
8. It can easily perform complicated tasks.

Difference between Hardwired Control and Microprogrammed Control

Hardwired Control	Microprogrammed Control
Technology is circuit based.	Technology is software based.
It is implemented through flip-flops, gates, decoders etc.	Microinstructions generate signals to control the execution of instructions.
Fixed instruction format.	Variable instruction format (16-64 bits per instruction).
Instructions are register based.	Instructions are not register based.
ROM is not used.	ROM is used.
It is used in RISC.	It is used in CISC.
Faster decoding.	Slower decoding.
Difficult to modify.	Easily modified.
Chip area is less.	Chip area is large.