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A computer is an electronic device that is used to accept the data, process the data and give desired information.

Computer hardware can be broken up into four parts:



Input and Output (I/O)


Functional Units:

Information Handled by a Computer

Instructions/machine instructions

  • Govern the transfer of information within a computer as well as between the computer and its I/O devices

  • Specify the arithmetic and logic operations to be performed

  • Program


  • Used as operands by the instructions

Source program

  • Encoded in binary code – 0 and 1

Memory Unit

  • Store programs and data

  • Two classes of storage

Primary storage

  • Fast, Programs must be stored in memory while they are being executed

  • Large number of semiconductor storage cells

  • Processed in words

  • RAM and memory access time

  • Memory hierarchy – cache, main memory

Secondary storage – Secondary storage, sometimes termed auxiliary storage, refers to the storage of data that is not accessed frequently as the data in primary storage. It is a non-volatile memory medium that preserves data until and unless it has been deleted or overwritten. Secondary storage might include hard disk drives (HDDs), solid-state drives (SSDs), optical disks, USB flash drives, floppy disks or other devices.

Arithmetic and Logic Unit (ALU)

  • Most computer operations are executed in ALU of the processor.

  • Load the operands into memory – bring them to the processor – perform operation in ALU – store the result back to memory or retain in the process

Control Unit

  • All computer operations are controlled by the control unit.

  • The timing signals that govern the I/O transfers are also generated by the control unit.

  • Control unit is usually distributed throughout the machine instead of standing alone.

Operations of a computer:

  • Accept information in the form of programs and data through an input unit and store it in the memory

  • Fetch the information stored in the memory, under program control, into an ALU, where the information is processed

  • Output the processed information through an output unit

  • Control all activities inside the machine through a control unit


The parts which go together to make up the computer system need to be able to communicate with one another. There are three sets of electrical lines which connect all the parts. These sets of lines are called buses. Bus is a subsystem that transfers data between components inside a computer, or between computers.

  • Here is a diagrammatic representation of a computer system. Note the direction of data flow between the different parts of the system.


1.Analog Computers: These are almost extinct today. These are different from a digital computer because an analog computer can perform several mathematical operations simultaneously.

2.Digital Computers: They use digital circuits and are designed to operate on two states, namely bits 0 and 1. They are analogous to states ON and OFF. Data on these computers is represented as a series of 0s and 1s. Digital computers are suitable for complex computation and have higher processing speeds. They are programmable. Digital computers are either general purpose computers or special purpose ones. General purpose computers, as their name suggests, are designed for specific types of data processing while general purpose computers are meant for general use. 3.Hybrid Computers: These computers are a combination of both digital and analog computers. In this type of computers, the digital segments perform process control by conversion of analog signals to digital ones

  • Mainframe Computers: Large organizations use mainframes for highly critical applications such as bulk data processing and ERP. Most of the mainframe computers have capacities to host multiple operating systems and operate as a number of virtual machines. They can substitute for several small servers.

  • Microcomputers: A computer with a microprocessor and its central processing unit is known as a microcomputer. They do not occupy space as much as

  • mainframes do. When supplemented with a keyboard and a mouse, microcomputers can be called personal computers. A monitor, a keyboard and other similar input-output devices, computer memory in the form of RAM and a power supply unit come packaged in a microcomputer. These computers can fit on desks or tables and prove to be the best choice for single-user tasks.

Computer sizes and power Computers can be generally classified by size and power as follows, though there is considerable overlap:

  • Personal computer: A small, single-user computer based on a microprocessor.

  • Workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and, in general, a higher-quality monitor.

  • Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously.

  • Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.

  • Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.

Information processing cycle The sequence of events in processing information, which includes (1) input, (2) processing, (3) storage and (4) output.

  • Input

This is the first event in the cycle. This stage involves collection of data from the outside or also from within the system.

  • Processing

In this stage the computer processes the minutest details entered. This processing makes the data entered usable. If the computer was not to process the data, it would not be of any use and it would also be a big mess of data.

  • Output

If you have to look at the diagram of information processing cycle, the step after processing is the output stage. The processed information is now transmitted to the user. This stage can also be further divided.

Types of software: Essential Computer Software

Operating Systems

  • The operating system is what allows you to interact with the PC, by acting as an interpreter between the machine language of the computer and you.


  • These types of software need an operating system in order to work.


  • The driver acts as a middleman between the operating system and the hardware in question, and allows the user to interact with the computer using the hardware

Programming Languages

  • Programming languages are a type of software that is used to create applications and operating systems.

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