how computer works

How Computer Works ?

If you are looking for simple introduction to how computer works then you have reached the right place . This is a step by step easy-to-understand introduction to how computer works.

The entire computer functions can be broadly grouped into four basic operations which includes input operations , storage operations  , data processing  and  output operations.

The computer system consist of both hardware components and the software components . The software provides a set of instructions which directs the various operations performed by the computer hardware components.

How Computer Works

This is a comprehensive step by step guide for you to  learn the entire logical sequence of operations performed by the computer system.

In this tutorial , you will also learn the various computer system components and how these components interact with each other when computer system is switched on.

How Does A Computer Work ?

Table Of Contents

What is a Computer System ?

A computer system is an electronic machine . A computer is designed to perform various used specified operations such as data processing , calculations , computer graphic , word processing and many such applications .

A computer basically operates by performing four basic operations . These basic computer operations include input operations , storage operations , data processing and output operations.

Computer System . How does a computer work
Computer System . How does a computer work

Computer Basic Operations

Input Operations

Storage Operations

Processing Operations

Output Operations

A computer is a digital electronic device because computer system can understand and execute only program instructions in binary .

A binary code is represented using binary number system in which each number is represented using only two numbers that is either numeric zero ( 0 ) or one ( 1 ).

How Computer Works ?

What is a Computer Hardware And Software ?

A computer system consist of various hardware and software components . The hardware components are tangible electronic and mechanical components.

Whereas , the software  components are the computer programs necessary to operate the computer hardware components and also to perform user specified other jobs on the system.

The user may use the computer for various operations such as data processing , word processing and other such applications.

The computer software can be broadly grouped into two categories that is system software and application software .

Application Software , How computer System Works
System Software , How computer system works

The system software components are used by the computer itself to operate and control the various hardware components and other hardware devices connected to the system .

Whereas, the application software are computer program specially created to allow the user to perform various operations such as creating documents , image editing , music players and other such utility programs.

How Computer Works ?

What is a Computer System Architecture ?

The computer system architecture defines the configuration of the computer system in terms of various components used , features and its specifications . The system architecture also defines the various performance parameter that system must achieve .

The system architecture does not specify any specific brand for various components rather it specifies the performance benchmarks .

In simple words , the system architecture is a blueprint for building a computer system in terms of components , configuration and technology .

Computer System Architecture

What is a Computer Program ?

A computer program is a set of instructions which directs the computer system. A computer performs various operations only as per the program instructions .

A computer program can be written in any programming language . However , the computer programs are generally written in using any high level programming language such as C language , C++ , Java , Python and other programming languages .

Since computer understands only machine code instructions in binary , a high level program first needs to be converted into machine code . This conversion process is referred as program compilation.

How computer works , Computer Coding, Computer Program Compilation

The binary machine code can be directly executed by the computer system . The low level machine code in binary consist of only patterns of 0 ( zero ) and 1 ( one ) .

And therefore , the computer programs are first written using a human friendly high level programming languages and then compiled to machine code in binary.

How Computer Works ?

What is Computer Program ?

What is an Operating System?

An operating system is an essential component of every computer system . It is a type of  system software that gets loaded first into the memory each time when the computer system is switched on .

An operating system is a system software that is responsible to manage the computer system . An OS provides a user friendly interface to the user to operate the computer system.

The operating system also performs some of the most important functions such as process management , system security , memory management , Resource management.

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What Is Operating System ?

Functions Of Operating System
Operating System Process Management

How Computer Works ?

What are Computer Hardware Components ?

The computer hardware components include of all the electronic components and also some mechanical components . Some hardware components are internal to the system.

These internal components are mounted inside a case . A computer case is a cabinet which provides a protective enclosure to the main system components.

Computer Hardware , How computer works
Computer System Hardware , How computer works

Some  hardware components are attached externally to the computer system . These external components attached to the system are also commonly referred to as peripheral devices .

The peripheral devices include input devices such as keyboard , mouse , scanner , camera and  other input devices . The standard output peripheral devices include display monitor , printer and external storage devices.

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What Is Computer Hardware ?

Computer Hardware Components

Computer System Hardware Components

How Computer Works ?

Computer Hardware Components

Computer System Case

Computer Case

The computer case ( cabinet ) provides a secured enclosed space to the system in which some of the most important system components are mounted.

The computer case also provides  secure mechanical slots in which various internal components can be placed .

The internal hardware components are placed inside  casing include  power unit ( SMPS ) , motherboard , micro-processor , graphics card , main memory RAM modules , hard disk , ventilation fan and other components.

Computer Case Types

Computer Case Types , Computer Case Form Factor

Microprocessor ( CPU )

The central processing unit ( CPU ) is the brain of the computer . The CPU is also alternately referred as microprocessor or simply processor.

The CPU is responsible to perform all the arithmetic calculations and logical operations . The CPU is securely mounted inside CPU socket present on the motherboard .

The CPU  mainly provides the processing power to the computer and therefore the system performance is significantly depends upon the processor type and speed .

Central Processing Unit ( CPU )

How Computer Works ?

What is Microprocessor ( CPU ) ?

Computer System Motherboard

The motherboard is the main circuit board inside the computer system .The motherboard  also works as a junction point where other vital components are connected to the system.

Some of the most important system components placed on the motherboard include microprocessor chip mounted inside a processor socket , the main memory RAM modules mounted inside slots , integrated controller chipset north bridge and south bridge  graphics card , BIOS and CMOS battery.

The motherboard also provide various connection sockets to connect the hard disk ( disk memory ) and other drives.


What Is Motherboard ?

Computer System Motherboard

Computer Main Memory

RAM - Random Access Memory

The main memory RAM is considered to be the main system memory. The Random Access Memory modules are mounted inside slots present on the motherboard.

The CPU starts the program execution only when it is loaded into the main memory. The most commonly used RAM size for is 4 GB , 8 GB  and 16 GB. 

The main system memory is a critical resource that is managed by the operating system . The main memory RAM is also referred as primary memory or volatile memory .

What Is Computer Memory ?

What is Computer Memory

Disk Memory ( Hard Disk )

The main memory RAM  has limited capacity and therefore , the computer makes use of another storage device called disk memory .

The disk memory is installed in the system either as hard disk inside the cabinet or as an external storage device .

The disk memory is considered to be the secondary memory. The hard disk  memory is mounted inside the specific mechanical slot inside the system casing.

The disk memory has relatively much higher capacity as compared to the main memory RAM and it is managed by the operating system . The disk memory is also referred as secondary memory or permanent ( Non-volatile ) memory .

Power Supply Unit ( SMPS )

The power supply unit ( SMPS – Switched Mode Power Supply ) is responsible to supply electricity current to various components as per the designated power supply requirement for each device.

The SMPS power supply unit is connected to the input power source ( 110 V US  , 220 V UK , India ) . The SMPS provides power output with multiple output wires for different internal system components .

This power supply to the system is managed and checked by the power unit    installed inside the computer cabinet .

How Computer Works ?

Input And Output Devices

The input and output devices are standard feature for almost all computer system .

Computer Input Devices
Computer System Devices
Computer Output Devices

Input Devices

The computer system use different types input devices which allow the user to interact with the computer system and accept the user input data .

The most commonly used input devices include keyboard , mouse , scanner , bar-code reader , camera , mic and other such devices.

Output Devices

The computer system use different types output devices to allow the user to use the processed data for different applications and display the processed data or store the data for future use.

The most commonly used Output devices include display monitor , printer , plotter , speaker and other such devices.

How Computer Works ?

What are Computer Software Components ?

The software is an essential feature of every computer system . The computer hardware components needs to be directed and controlled with the help of programs also called software.

The computer system use two types of  software components which includes both application software and system software.

Application Software

The application software are designed to provide various functionality . The user needs different types of application software to perform various operations .

For example , the most commonly used application software include Microsoft Office . The MS Office internally consist of group of software  and each provides a specific functionality to the use such as MS Word , Power Point and MS Excel.

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What Is Application Software ?

System Software

The system software is an essential component of every computer system . The operating system  is the most commonly used operating system present in every computer .

The operating system internally use other system software components such as device drivers and system utility programs.

The operating system interacts with various hardware components with the help of another system software called the device driver.

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What Is System Software ?

So far we have learned the basics of computer system , various software and hardware components and the functions performed by these components.

The entire computer functions can be broadly grouped into four basic operations which include input operations , storage operations  , data processing  and output operations

Let us now understand how computer works step by step and the interaction that happens  between the various components after the system is powered on.   

How Computer Works ?

How Computer Works - Step By Step

The computer performs power supply check ( POST ).

When the computer system is first powered on , the first job for the computer is to ensure that the computer is getting adequate and designated power supply to the system .

The system power supply unit carries out self-test called POST. The POST stands for  “Power On Self Test” .

The POST test checks the computer systems internal hardware for compatibility , connection  and  ensures that no errors exist before loading the operating system .  

Operating System Booting , POST Test
Operating System Booting , POST Test

Only after  successful completion of the POST ,  the bootstrap loader  routine  on the  BIOS  chip is  invoked  to  load  the  operating  system  . If the POST fails then the computer system  will  beep for different   beep codes .

After successfully completing the POST (  Power On Self Test ) , the BIOS  then  attempt to loads the operating system ( OS )  into the main system memory  RAM  ( Random Access Memory ).

The OS is located either on the internal hard disk  attached to the computer system  OR  from bootable OS disk in the CD ROM drive. The BIOS will pass the control to the operating  system  once  the it  is  fully  loaded

The CPU Activates the BIOS to Initiate the Booting Process.

The user can start using the computer when the operating system is fully loaded and operational . And therefore , the  microprocessor’s first  job  is to locate and  initiate the process of loading the  operating  system  every time the computer system  is switched  on .

The CPU loads the Operating system  with the help of another system  utility program called  BIOS  (  Basic Input Output System  ) .

BIOS stands for Basic Input Output System. The BIOS is a system utility program which loads the operating system when computer is switched on. Learn More :


BIOS Chip , what is UEFI
BIOS Chip , what is UEFI

The Operating System Loads Program into the Main Memory ( RAM ).

The operating system allocates the necessary resources in terms of memory ( RAM ) and the processor time required for the program execution.

The operating system then loads the executable copy of the program ( machine code instructions ) and associated data into the main memory RAM .

The operating system efficiently manages the memory requirement needed for different processes running on the system .

The OS makes use of virtual memory which is an internal mechanism to accommodate the memory requirement for the processes that exceeds the available main memory RAM .

How Computer Works ?

The CPU Initiates the Program Execution .

The microprocessor is the brain of the computer system which provide the processing power and the decision making ability to the system .

The CPU initiates the program execution by fetching the program instructions and the data from the main memory RAM .

The CPU executes the program instructions one by one and operates on the data as per the program instruction .

CPU Machine Cycle

In order to execute the program , the CPU repetitively performs a sequence of four steps called machine cycle . The machine cycle steps include :

1. FETCH     2. DECODE    3. EXECUTE    4. STORE

The processed data after the CPU operation is sent back and stored into the main memory . This processed data can be sent to any output device such as display monitor or printer or secondary storage device for future use.


What Is Machine Cycle ?

CPU Instruction Cycle

The computer program is a set of instructions which directs the computer hardware to perform various user defined operations. 

The instruction cycle is the time required by the CPU to execute one program instruction. It is the time taken by CPU to fetch , decode and execute one single instruction.

Depending upon the processor architecture , the processor takes either one or more machine cycle to complete one instruction cycle. 


What Is Instruction Cycle ?

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