Block Diagram of Computer

A Block diagram of a computer displays a structural representation of a computer system. The block diagram gives you a quick overview of the working process of a computer from inputting the data to retrieving the desired results.

The following diagram represents a block diagram of the computer system:

Block Diagram of Computer

A computer system is a combination of three components:
Input Unit
CPU (Central Processing Unit)
Output Unit

Input Unit

The Input Unit consists of input devices such as a mouse, keyboard, scanner, joystick, etc. These devices are used to input information or instruction into the computer system. Like other electronic machines, a computer takes inputs as raw data (binary data) and performs necessary processing giving out processed data. Therefore, the input unit is the medium of communication that takes data from us to the computer in an organized manner for processing.

The Input Unit performs the following major functions:

The input unit converts the inputted data or instructions into binary form for further processing.
Input Unit transmits the data to the main memory of the computer.

Central Processing Unit

CPU or Central Processing Unit is known as the brain of the computer system. It is an electronic hardware device that processes all the operations (e.g., arithmetic and logical operations) of the computer. In other words, all the major calculations, operations or comparisons are performed inside the CPU. It is also responsible for handling the operations of several other units.
CPU (Central Processing Unit) Structure Diagram

In the above diagram, the Control Unit (CU) and Arithmetic & Logic Unit (ALU) are jointly called the Central Processing Unit (CPU).

Let's discuss all the parts displayed in the above diagram one by one:

Control Unit

As the name suggests, the control unit of a CPU controls all the activities and operations of the computer. It is also responsible for controlling input/output, memory, and other devices connected to the CPU.

The control unit acts like the supervisor which determines the sequence in which computer programs and instructions are executed. It retrieves instructions from memory, decodes the instructions, interprets the instructions and understands the sequence of tasks to be performed accordingly. It further transmits the instructions to the other parts of the computer system to execute them. In short, the control unit determines the sequence of operations to execute the given instructions. 

Arithmetic & Logic Unit

The data inputted through input devices is stored in the primary storage unit. The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations. 

The arithmetic unit controls simple operations such as addition, subtraction, division, and multiplication.

On the other side, the logical unit controls the logical operations such as AND, OR, Equal, greater than, and less than, etc. Apart from it, the logic unit also responsible for performing several other operations such as comparing, selecting, matching, and merging data.

The information or data is transmitted to ALU from the storage unit only when it is required. After completing the operations, the result is either returned to the storage unit for further processing or getting stored.

Memory Unit

Memory Unit is an essential part of the computer system which is used to store data and instructions before and after processing.  The memory unit transmits the information to other units of the computer system when required.

There are two types of memory units:

Primary Memory

The primary memory cannot store a vast amount of data. The data stored in the primary memory is temporary. The data will be lost if they are disconnected from the power supply. The primary memory usually stores the input data and immediate calculation results. The primary memory is also known as the Main Memory or temporary memory. Random Access Memory (RAM) is an example of primary memory. 

Secondary Memory

The use of primary memory is not possible to store data permanently for future access. Therefore, there are some other options to store the data permanently for future use, which is known as secondary memory or auxiliary storage or permanent storage. The data stored in the secondary memory is safe even when there is a power failure or no power supply. Hard Disk is usually considered a secondary memory.

Note: Primary memory is the only memory that is directly accessible to the CPU. Secondary memory is not directly accessible to the CPU. The data accessed from the secondary unit is first loaded into RAM and then further transferred to the Processing Unit. The use of different memory units depends entirely on the size of the data.

The Central Processing Unit performs the following major functions:

The CPU controls all components, software and data processing of the computer system.
The CPU takes data from input devices, executes the data, and sends output to the output devices.
The CPU processes all the operations, including all the arithmetical and logical operations.

Output Unit

The output unit consists of devices that are used to display the results or output of processing. The output data is first stored in the memory and then displayed in human-readable form through output devices. Some of the widely used output devices are Monitor, Printer, and Projector.

The Output Unit performs the following major functions:

The output unit accepts the data or information in binary form from the main memory of the computer system.
The output unit converts the binary data into a human-readable form for better understanding.


The set of data or instruction is entered through input devices in the form of raw data or binary data.
The instruction is processed with the help of the central processing unit, the combination of a control unit and the arithmetic & logic unit.
The computer system produces the output with the help of output devices, which converts retrieved binary data into human-readable form.
Throughout the entire process, the data is stored in the memory unit, either primary or secondary, depending on the size of the data.

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