Introduction to Control Unit

A control unit, or CU, is circuitry within a computer’s processor that directs operations. It instructs the memory, logic unit, and both output and input devices of the computer on how to respond to the program’s instructions. CPUs and GPUs are examples of devices that use control units.

In this article, we will dive deeper into the Control Unit according to the GATE Syllabus for (Computer Science Engineering) CSE. Keep reading ahead to learn more.

Table of Contents

What is a Control Unit in Computer Architecture?
How Does a CPU Control Unit Work?
The Function of Control Unit
Control Unit Types
- Hardwired Control Unit
- Micro Programmable Control Unit
Practice Problems in Control Unit
Frequently Asked Questions in Control Unit

What is a Control Unit in Computer Architecture?

The CPU control unit is a component of the computer’s CPU (central processing unit) that directs the processor’s operation. John von Neumann included it in his Von Neumann Architecture. The control unit’s job is to instruct the computer’s arithmetic/logic unit, memory, and input and output devices on how to respond to the instructions supplied to the processor.

Introduction-to-Control-Unit

The control unit fetches internal program instructions from the main memory to the processor instruction register, and it generates a control signal based on the contents of this register to supervise the execution of these instructions.

How Does a CPU Control Unit work?

A control unit receives data from the user and translates it into control signals that are subsequently delivered to the central processor. The processor of the computer then instructs the associated hardware on what operations to do. Because CPU architecture differs from manufacturer to manufacturer, the functions performed by a control unit in a computer are dependent on the CPU type. The following are some examples of devices requiring a control unit:

CPUs or Central Processing Units
GPUs or Graphics Processing Units

Introduction-to-Control-Unit-1

The Function of Control Unit

It coordinates the flow of data out of, into, and between the various subunits of a processor.
It understands commands and instructions.
It regulates the flow of data within the processor.
It accepts external commands or instructions, which it turns into a series of control signals.
It is in charge of a CPU’s multiple execution units (such as ALUs, data buffers, and registers).
It also performs a variety of activities, including fetching, decoding, handling execution, and storing results.

Control Unit Types

The design of the control unit depends on the type of control unit in use. Here are the types of control units:

Hardwired Control Unit

The control signals that are necessary for instruction execution control in the Hardwired Control Unit are generated by specially built hardware logical circuits, and we can’t change the signal production mechanism without physically changing the circuit structure. Read more on Hardwired Control Unit here.

Micro Programmable Control Unit

The existence of the control store, which is used to store words containing encoded control signals required for instruction execution, is the main distinction between the unit structure and the hardwired control unit structure. Read more on Microprogrammed Control Unit here.

Practice Problems in Control Unit

1. Which of these isn’t a computer’s characteristic?

a. I.Q.

b. Diligence

c. Versatility

d. Accuracy

Answer – (a) I.Q.

2. Which of these refers to a set of microinstructions for just a single machine instruction?

a. Micro command

b. Micro program

c. Command

d. Program

Answer – (b) Micro program

Frequently Asked Questions in Control Unit

What is a control unit? Explain with an example?

What are ALU and CU?

The difference between CU and ALU is that an arithmetic logic unit or ALU is a processor component that conducts arithmetic operations, comparison, and various other operations. While the control unit or CU is the part of a processor that directs and controls the majority of the computer’s operations.

What is a Memory Unit?

The memory unit is the quantity of data that is stored in a storage unit. Bytes are used to measure the storage capacity.

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