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Computer, its Types and Anatomy

A Computer is an electronic device that can perform activities which involve mathematical computations, logical operations, and graphical manipulations. Generally, the term "Computer" is used to describe a collection of devices that function together as a system.It performs the following three operations in sequence:

  1. Receives data & instructions from the input device.
  2. Processes the data as per instructions.
  3. Provides the output (result) in a desired form.

A computer is a programmable electronic device(machine) that takes raw facts as input, process them and gives the final output which is the result of processing. It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program).

Data: It is the collection of raw facts, figures & symbols to be processed.Ex: Names of teachers and their salary in different subjects listed in random order.
Information: It is the data that is processed & presented in an organized manner. The processed data are known as information.Ex: When the names of students of a class are arranged in alphabetical order, total marks and average marks obtained are calculated & presented in a tabular form, it is the information.
Program: Set of instructions that enable a computer to perform a given specified task.

Characteristics of computers

High speed: Computers have the ability to perform routine tasks at a greater speed than humans. They can perform millions of calculations in few seconds.
Accuracy: Computers are used to perform tasks in such a way that ensures accuracy. Computers give accurate results as per the activities performed.
Storage: Computers can store a large amount of data & information. Any item of data or any instruction stored in the memory can be retrieved(again be used) by the computer at lightning speeds.
Automation: Computers can be instructed to perform complex tasks automatically (that increases the productivity).
Diligence: Computers can perform the same task repeatedly & with the same accuracy without getting tired or bored.
Versatility: Computers are flexible to perform both simple and complex tasks. So they are also called versatile machines.
Cost effectiveness: Computers reduce the amount of paperwork and human effort, thus reducing the costs.

Limitations of computers

  1. Computers need clear and complete instructions in order to perform a task accurately. If the instructions are incomplete & not clear, then the computer will not produce the required result/output.
  2. Computers cannot think on its own.
  3. Computers cannot learn by experience.

Classification of Digital Computers (Types of Computers)
Computers can be classified by their size and power as drafted below:

  1. Super Computers
  2. Mainframe Computers
  3. Mini Computers
  4. Work Stations
  5. Micro Computers/ Personal Computer
  6. Network computers

Super Computers

  • The primary application of supercomputers has been in scientific and military work, but their use is gradually growing in business as their prices decrease.
  • They are especially valuable for large simulation models of real world phenomena, where complex mathematical representations and calculations are required or for image creation and processing.
  • They are also used in weather prediction, designing aircraft ( Boeing 777), motion pictures like star wars and JurassicPark).
  • They operate generally at 4 to 10 times faster than the next most powerful computer class., the mainframe.

Mainframe Computers

  • They are less powerful and generally less expensive than supercomputers.
  • Large corporate use mainframe computers for centralized data processing maintaining large databases.
  • Application than run on a mainframe can be large and complex, allowing for data and information to be shared throughout the organization.
  • Examples: Airline Reservation System, Corporate Payroll, etc.
  • A mainframe system may have anywhere from 50megabytes to several GBs(gigabytes) of primary storage.
  • Secondary storage may use high capacity magnetic and optical storage media with capacities in the GBs(gigabytes) to TBs(terabytes) range.
  • Typically, several hundred or thousands or online computers can be linked to a mainframe.
  • Advance mainframe performs more than 1,000 MIPS and can handle up to a billion transactions per day.

Mini Computers

  • Also called midrange computers, are relatively small, inexpensive and compact computers that perform the same functions as mainframe computers but does so to limited extent.
  • They are designed especially for accomplishing specific tasks like process control, scientific research, and engineering applications.
  • IBM is the market leader in minicomputers with its AS/400 series of computers.
  • Larger companies gain greater corporate flexibility by distributing data processing with minicomputers in various organizations units instead of centralization at one place.
  • They form the network.


  • Computers vendors originally developed desktop engineering workstations or to provide the high levels of performance demanded by engineers.
  • They have based on RISC (Reduced Instruction Set Computing) architecture and provide both very high-speed calculations and high-resolution graphic displays.
  • The distinction between workstation and PCs is rapidly blurring.
  • The latest PC's has the computing power of recent workstation.

Micro Computers
These are also called PCs(Personal Computers). They are the smallest and least expensive category of general purpose computers. Microcomputer ranges from palmtops to Desktop computers in size. Laptops/ Notebooks are very popular nowadays. The microprocessor is the core part of the Microcomputers which forms the CPU.

Network Computers
A computer with minimal memory, disk storage and processor power designed to connect to a network, especially the Internet is a Network Computer. The idea behind network computers is that many users who are connected to a network do not need all the computer power they get from a typical PC(Personal Computer). Instead, they can rely on the power of the network servers. This is really a variation on an old idea -- diskless workstations -- which are computers that have memory and a processor but no any disk storage. Instead, they rely on a server to store data. Network computers take this idea one step further by also minimizing the amount of memory and processor power required by the workstation. Network computers designed to connect to the Internet are sometimes called Internet boxes, Net PCs, and Internet appliances.

Anatomy of Digital Computers:

Block Diagram of a Digital Computer

The CPU is the “brain” of the computer, the place where data is manipulated. In larger computer systems, such as supercomputers and mainframe computers, processing task may be handled by multiple processing chips. In the average microcomputer, the entire CPU acts as a single unit called a microprocessor. Every CPU has at least two parts: the control unit (CU) and the arithmetic and logic unit (ALU).

The Control Unit (CU)
All the resources of the computer are managed by the control unit. The control unit controls the data flow through the CPU, and to and from other devices. The control unit is the logical hub of the computer.


The Arithmetic and Logic Unit (ALU)
Many instructions which are carried out by the CU involve simply moving data from one place to another from memory to storage, from memory to the printers and so on. When the control unit encounters an instruction that involves arithmetic or logic, however, it passes the instruction to the second components of the CPU, the arithmetic and logic unit or ALU. The ALU actually performs the arithmetic operations (+,-,X, ÷) and the logical operations (=,>,<,>=,<=,!= etc). The ALU includes a group of registers- high-speed memory locations built directly into the CPU that is used to hold data currently being processed.

In microcomputers, the term "bus" refers to the path between the various components of a computer. There are two main buses in a computer: the system (or internal) bus and the expansion ( or external) bus. The system bus resides on the motherboard and connects the CPU to other devices that reside on the motherboard. An expansion or external bus connects external devices, such as the keyboard, mouse, modem, printer etc to the CPU. Cables from disk drives and some other internal devices may also be plugged into the bus.

Functions and Components of a Computer:
In order to function properly, the computer needs both hardware and software. Hardware consists of the mechanical and electronic devices, which we can see and touch. The different parts of the computer are Processor (CPU), Input devices, Output devices, Storage devices and Memory devices. The software consists of programs, the operating systems(OS) and the data that reside in the memory and storage devices.Computer hardware falls into two categories: processing hardware, which consists of the central processing unit (CPU), and the peripheral devices. The CPU, as its name implies, is where the data processing is done. Peripheral devices allow the user to interact with the CPU. Together, they make it possible to use the computer for a variety of tasks.

A computer mainly does the following four functions:

  • Receive input – Accept information through various input devices like the keyboard, mouse, lightpen, etc.
  • Produce information – Perform arithmetic or logical operations on the information.
  • Produce output – Communicate information to the outside world through various output devices like monitor, printer, plotter, etc.
  • Store information – Store the information in storage devices like hard disk, floppy disks, pen drives, etc.

Working of CPU and memory
An instruction is fetched from primary storage by the Control Unit(CU). The Control Unit decodes the instruction. The ALU receives the data and the instruction and performs the calculation or comparison. The result is stored in primary storage which is sent to the proper output device.


  • Note by - Kumar Poudyal
  • Text Books- Alexis Leon, Mathews Leon, Fundamentals of Information Technology, Leon TechWorld
  • Website- www.csitnepal.com



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