Computer System || Computer Architecture


A system is a group of related components that have a common purpose of achieving some objectives. Computer system is a combination of interconnected devices that share central storage and various peripherals as a whole. The computer is a system because it is a group of integrated parts they work together to perform varieties of tasks. A computer has various units. Each unit performs a specific function in the computer. A computer system can be defined as: The computer along with various hardware units and software that makes the computer function and performs the different tasks is collectively known a computer system.

The computer system is in-complete without the involvement of any operate computer are known as users. Computer is not totally autonomous. Even if the computer can do its job without the person sitting in front of it. People involve in design, build and repair computer program and system. Therefore, a complete computer system consists of four parts. They are:

  • Computer Hardware
  • Computer Software
  • Data
  • User

A group of hardware components and associated software are designed and assembled to perform a specific function or group of functions in the computer. The user is the main handler of computer system. The data are the main thing that process the computer to convert into useful information.

computer hardware

The physical parts of a computer are known as computer hardware. The hardware consists of electronic circuits and all the devices used to perform various functions in the computer system. Hardware are such parts of computer that we can see, touch, and feel. Some examples of hardware are: keyboard, mouse, monitor, system unit and its components, printer, scanner, microphone, web camera, joystick, etc.

Types of Computer Hardware

The hardware components of computers differ from one computer model to another. However, the basic components and their functions are the same for all computer systems. The computer hardware can be categorized into four different types. They are:

  • Input Unit
  • Output Unit
  • Processing Unit
  • Memory and Storage Unit

The following block diagram shows how hardware components are interconnected witheach other in computer is also known as computer architecture.

Computer System || Computer Architecture

Input Unit

The input unit consists of input devices. The devices that are used to enter data and instructions or commands into the computer are called input devices. With the help of input devices, we can enter data and give commands to the computer. Keyboard, mouse etc. are the common input devices.

Processing Unit

The Processing unit consists of Processing devices. Central Processing Unit (CPU) is the main processing unit of the computer, so it is also considered as an electronic brain of computer. It performs all operations of data according to program’s instructions. It executes the program instructions and tells other parts of the computer what to do. The speed of the CPU is measured in Mega Hertz (MHz) or Giga Hertz (GHz) or more. The CPU consists of three main parts. These are:

  • Control Unit (CU)
  • Arithmetic Logic Unit (ALU)
  •  Registers

Control Unit (CU)

The control unit is the most important component of the CPU, It controls and coordinates the activities of all the other units of the computer. The control unit acts as central nervous system and controls the execution of instructions given to the computer. It fetches the instructions and data from the memory unit and executes the instructions one by one.

Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit (ALU) is another important component of CPU, It performs the arithmetic and logical operations on the data. When the control unit encounters instruction related to perform arithmetic or logical operation on data, it passes that instruction to ALU. In arithmetic operations ALU performs the addition, subtraction, multiplication and division. In logical operations ALU compares the numerical data as well as alphabetic data. For example, it checks whether the first number is greater than the second, less than the second or equal to the second, etc.


Register is a small amount of storage available as a part of CPU. The CPU also consists of a number of registers and adder circuits. A register is a temporary storage device which holds data and instruction as long as it is being interpreted and executed. When the data and instructions are fetched from the main memory for processing, these have to be stored in one of the registers of the CPU.

Output Unit

The output unit consists of output devices. The output devices are the hardware components used to get output from the computer. The processed result of the computer is  called output. A computer generates several types of output, depending upon the hardware and software used and the requirements of the user. We can see output on a screen, print it on the printer or hear it through speakers. Monitor, printer etc. are the common output devices.

Difference between Input and Output devices

Input devices Output devices  
1. They are used to input data  1. They are used to provide the result in understandable form  
2. They convert data into computer2. They convert data into human understandable form  
3. e.g. Keyboard, Mouse  3. e.g. Monitor, Printer  

Read more : Input Output Devices

Memory and Storage Unit

The devices that are used to store the data and program instructions either temporarily or permanently are included in memory and storage unit. Both memory and storage device are used to store data and instructions but their purpose is different. The purpose of storage devices is to store data permanently even when the computer is switched off. The purpose of memory devices is to store data either temporarily or permanently while the computer works with them. The memory unit is also called the primary storage and the storage unit is also called the secondary storage or mass storage. The two most important memory devices are:

  • Random Access Memory (RAM)
  • Read Only Memory (ROM)

The most commonly used storage devices are:

  • Floppy Disk (Diskette)
  • Hard Disk
  • Pendrive
  • Memory card
  • CD- ROM

Computer Software

Software is the major part of computer system that is used to operate the computer. It enables the computer to do work. It is not possible to operate the computer without software. It instructs all the physical parts of computer system what task it should perform and how. It is such a part of  computer system that we cannot see, feel or touch. So, software is the collection of programs which make computer system work.


Data are the unarranged or unprocessed raw facts and figures which may give or may not give much sense or meaning to the user. Data are represented by sign, symbol, number or alphabets. We get meaningful information only after processing data. Data can be processed manually or electronically. The electronic data processing is done using the electronic devices like computer For example the data “shuman, boy, Pokhara, loksewa computer operator,” do not give any clear meaning. However if these individual data are arranged in a sentence like “shuman is a boy , he lives in Pokhara and he is preparing for loksewa computer operator “, now we could probably make sense of it. This is an example of data being processed into meaningful information.


Person who operate the computer are known as users. Generally, people used to say that computer has done this and that but actually this is not the computer has done itself but this has done by the user. User is the main handler of the computer system. The computer system is incomplete complete without involvement of any user.

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