Block Diagram of a Computer

With technology upgrading rapidly, computers have now become part of our daily lives.

From performing basic operations like watching a movie to high-level functions like manufacturing a car, computers are doing it all.

But have you ever thought about how does a computer works? What processes go inside it that makes even a tough task seem easy. Just like the other machines, the computer has also a basic architecture that comprises multiple elements that process the input and produce the desired output.

Let us look at the basic block diagram of the computer and understand how each part contributes to its functioning.

Block diagram of a computer


All the data received by the computer goes through the input unit. The input unit comprises devices like a mouse, keyboard, scanner, etc. Each of these devices acts as a mediator between the users and the computer.

The data that is to be processed is put through the input unit, the computer accepts the raw data in the binary form, processes the data, and produces the desired output.

The 3 major functions of the input unit are-

  • Take the data to be processed from the user.
  • Convert the given data into machine-readable form.
  • Transmit the converted data into the main memory of the computer. Its sole purpose is to connect the user and the computer and create easy communication between them.

CPU – Central Processing Unit

Central Processing Unit or the CPU, is the brain of the computer. It works the same way a human brain works. all the activities performed by humans are controlled by the brain. Similarly, all the functions/tasks performed by the computer are controlled by the CPU.

All the logical and arithmetical operations conducted by the computer are carried out by the working of the CPU.

Now the CPU comprises of two units, namely- ALU (Arithmetic Logic Unit) and CU (Control Unit). Both of these units work in sync so that the CPU processes the data as a whole. Let us see what particular tasks are assigned to both units.

ALU – Arithmetic Logic Unit

The Arithmetic Logic Unit is made of two terms, arithmetic and logic. So as the name suggests there are two major functions that this unit performs.

  1. It takes the data inserted by the input unit into the primary memory and performs the basic arithmetical operation on it. Like additions, subtraction, multiplication, and division. It performs all sorts of calculations required on the data and then sends back it to the storage.
  2. The unit is also responsible for performing logical operations like, AND, OR, Equal to, Less than, etc.  In addition to this it conducts merging, sorting, and selection of the given data.

CU – Control Unit

The control unit as the name suggests is the controller of all the activities/tasks and operations performed inside the computer.

The memory unit sends a set of instructions to the control unit. The control unit in turn converts those instructions into control signals. These control signals help in prioritizing and scheduling the activities that are being performed by the computer. Thus, the control unit coordinates the tasks inside the computer in sync with the input and output units.

Memory Unit

All the data that has to be either processed or has been processed is all stored in the memory unit. The memory unit acts as a hub of all the data and transmits it to the required part of the computer whenever necessary.

The memory unit works in sync with the CPU. This helps in faster accessing and processing of the data, thus makes tasks easier and faster. There are two types of computer memory-

  1. Primary memory – This type of memory cannot store a vast amount of data, therefore is only used to store recent data. The data stored in this is temporary and can get erased once the power is switched off. The Primary memory therefore is also called the temporary memory or the main memory.

    RAM stands for Random Access Memory, it is an example of primary memory. This memory is directly accessible by the CPU for reading and writing purposes. For data to be processed, it has to be first transferred to the RAM and then to the CPU.

  2. Secondary memory – As explained above, the primary memory stored temporary data, thus it cannot be accessed in the future. For permanent storage purposes, the secondary memory is used, also called the permanent memory or the auxiliary memory. The hard disk is an example of the secondary memory and data in this memory does not get erased easily even in a power failure.


There is nothing to be amazed by what the output unit is used for. All the information sent to the computer once processed is received by the user through the output unit. Devices like printers, monitors, projector, etc. all come under the output unit.

The output unit displays the data either in the form of a soft copy like that in the monitor or the form of a hard copy, through a printer. The output unit first accepts the data in the binary form from the computer and then converts it into a readable form for the user.


Let us finally look at what the data flow looks like inside the computer step by step-

  1. The data is accepted by the input unit, given by the user. It is then converted into binary form for the computer to read it.
  2. The information is then sent to the memory unit for storage and processing.
  3. The required data, that needs to be processed is accessed by the CPU from the primary storage. The arithmetic and logical operations are then performed on the data. The control unit schedules all the activities for the smooth working of the computer.
  4. The data is then again sent to the storage unit for storing or further processing purposes.
  5. The final processed output is received through the output unit.

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