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Types of Computer

We can categorize computer by three ways:

  1. Based on data handling capabilities
  2. Based on size
  3. Based on Utility

 On the basis of data handling capabilities, the computer is of three types:

  1. Analogue Computer: Analogue computers are designed to process the analogue data. Analogue data is continuous data that changes continuously and cannot have discrete values. Analogue computers directly accept the data from the measuring device without first converting it into numbers and codes. Speedometer and mercury thermometer are examples of analogue computers.
  2. Digital Computer: Digital computer is designed to perform calculations and logical operations at high speed. It accepts the raw data as digits or numbers and processes it with programs stored in its memory to produce output. All modern computers like laptops and desktops that we use at home or office are digital computers.
  3. Hybrid Computer: It is a combination of Analog and Digital computer.

On the basis of size, the computer can be of four types:

  1. Microcomputer: Microcomputer is also known as personal computer. It is a general purpose computer that is designed for individual use. It has a microprocessor as a central processing unit, memory, storage area, input unit and output unit. Laptops and desktop computers are examples of microcomputers. Desktop Computer, Laptop Computer, Palmtop Computer/Digital Diary /Notebook /PDAs
  2. Mini Computer: Minicomputers possess most of the features and capabilities of a large computer but are smaller in physical size. They are used as small or midrange operating business and scientific applications.
  3. Mainframe computer: Mainframe computers are designed to support hundreds or thousands of users simultaneously. They can support multiple programs at the same time. It means they can execute different processes simultaneously. These features of mainframe computers make them ideal for big organizations like banking and telecom sectors, which need to manage and process high volume of data
  4. Supercomputer: Supercomputers are the biggest and fastest computers. They are designed to process huge amount of data. A supercomputer can process trillions of instructions in a second. It has thousands of interconnected processors. First supercomputer was developed by Roger Cray in 1976.

Features of Word Processor

  • OLE (Object Linking and Embedding) OLE is a program integration technology that is used to share information between programs through objects. Objects are saved entities like charts, equations, video clips, audio clips, pictures etc.
  • Mail merge is a feature within most data processing applications that enables users to send a similar letter or document to multiple recipients.
  • Title Bar: It shows the name of the file on which you are working. It also consist of three buttons, eg,
  • Minimize button reduces the window to an icon but word still remains active.
  • Restore button again brings word window to the maximum original size.
  • Close button brings us out of word.
  • Menu Bar: It consists of various commands which can be accessed by clicking at the menu options under these menu heads.
  • Standard Tool Bar: It displays the symbols for the common operation like open, print, save etc which can be per formed by clicking on the appropriate tool.
  • Formatting Tool Bar: It displays the options which can be used to format our document like font type, size of the font, bold, underline, bullets, alignment etc.
  • Ruler: It shows the width of the document. It can be increased or decreased. You can see how much of the lines you have consumed by typing.
  • Workspace: It is the area where the text can be entered.
  • Vertical Scroll Bar: For a larger text in the document, you can scroll the vertical bar to see the text at various position.
  • Horizontal Scroll Bar: It is used to move from left side to right side in the document and vice-versa in case the document is too wide to fit in the screen.


MS Excel

  • Worksheet: It is a grid of cells made up of horizontal rows and vertical columns. Worksheet contains 65,536 rows and 256 columns.
  • Row Number :Each row is given a number that identifies it, starts from 1, 2, 3, 4, … so on.
  • Column Letter: Each column is given a letter that identifies it, starts from A … Z, AA … AZ, BA … BZ, …IA – IV.
  • column in table can also be referred to as a field.

Generations of Computer

First Generation: The hardware used in the first generation of computers were: Vacuum Tubes, Punch Cards.

It supported machine language. The memory was of 4000 bits.

The examples of first generation computers are: ENIAC, UNIVACTBM 701, IBM-701, IBM-650.

Second Generation:

The hardware used in the second generation of computers were: Transistors, Magnetic Tapes

It Supported Batch operating system.

The capacity of the memory was 32,000 bits.

The examples of second generation computers are −

Honeywell 400, CDC 1604, IBM 7030

Third Generation

The hardware used in the third generation of computers were: Integrated Circuits made from semi-conductor materials, Large capacity disks and magnetic tapes

Supports time-sharing OS, 128,000 bits, the input was provided through keyboards

The examples of third generation computers are: IBM 360/370, CDC 6600, PDP 8/11

Fourth Generation

The Hardware used in the fourth generation of computers were: ICs with Very Large Scale Integration (VLSI) technology, Semiconductor memory, Magnetic tapes and Floppy.

Multiprocessing & distributed OS, Object-oriented high level programs supported, No external cooling required & affordable

Storage System in Computer

There are three main types of secondary storage in a computer system:

  1. Solid state storage devices (such as USB memory sticks): Solid state storage is also faster than traditional hard disk drives because the data is stored electrically in silicon chips called cells. Within the cells, the binary data is stored by holding an electrical current in a transistor with an on / off mode. 
  2. Optical storage devices (such as CD, DVD and Blue-ray discs): Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into tracks, with each track containing many flat areas and hollows. The flat areas are known as lands and the hollows as pits. 
  3. Magnetic storage devices (such as hard disk drives): Magnetic devices such as hard disk drives use magnetic fields to magnetize tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetized section represents a binary '1' and a demagnetized section represents a binary '0'.

Keys on keyword: 

  • Typing Keys: These keys include the letter keys (A-Z) and digit keys (09) which generally give the same layout as that of typewriters.
  • Numeric Keypad: It is used to enter the numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
  • Function Keys: The twelve function keys are present on the keyboard which is arranged in a row at the top of the keyboard. Each function key has a unique meaning and is used for some specific purpose.
  • Control keys: These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc)
  • Special Purpose Keys: Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.

Some other important terms:

File: A file is a collection of logically related information.

Features of DOS

  • It is not case sensitive, ie, DIR and dir are treated as the same.
  • The file names are restricted to 8 characters only.
  • It does not support space entries in the file name.

History of computer:

The history of computer begins with the birth of abacus which is believed to be the first computer. It is said that Chinese invented Abacus around 4,000 years ago.

In the early 1820s, it was designed by Charles Babbage who is known as "Father of Modern Computer". It was a mechanical computer which could perform simple calculations.

The abacus was the first device for mathematical calculation. It can perform addition and subtraction.

John Napier invented logarithms, which is a technique that allows multiplication of the number via addition using a printed table.

Charles Babbage proposed a steam driven calculating machine the size of a room, which he called the Difference Engine. UNIVAC is the first commercial computer. In the 50's

UNIVAC called is Universal Automatic Computes was the household word for Computer UNIVAC was also the first computer to employ magnetic tape.

Important Input Devices 

  • Magnetic Ink Character Recognition (MICR): MICR computer input device is designed to read the text printed with magnetic ink. It is widely used in banks to process the cheques and other organizations where security is a major concern.
  • Optical Character Reader (OCR): OCR computer input device is designed to convert the scanned images of handwritten, typed or printed text into digital text. It is widely used in offices and libraries to convert documents and books into electronic files.
  • Optical Mark Reader (OMR): OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked.



The printers are of two types: 

  1. Impact Printers
  2. Non-impact Printers.

Impact Printers: They are of two types:

Character Printers (Dot Matrix printers, Daisy Wheel printers) and Line printers (Drum printers, Chain printers)

Non-impact printers: They are of two types: Laser printers, Inkjet printers.

Impact Printer: The impact printer uses a hammer or print head to print the character or images onto the paper.

Non-Impact Printer: They print characters and images without direct physical contact between the paper and the printing machinery. These printers can print a complete page at a time, so they are also known as page printers. The common types of non-impact printers are Laser printer and Inkjet printer:

Multiprogramming and Multiprocessing Operating System

Multiprogramming Operating System:

Multiprogramming is an extension to the batch processing where the CPU is kept always busy. Each process needs two types of system time: CPU time and IO time. In multiprogramming environment, for the time a process does its I/O, The CPU can start the execution of other processes. Therefore, multiprogramming improves the efficiency of the system.

Multiprocessing Operating System:

In Multiprocessing, Parallel computing is achieved. There are more than one processors present in the system which can execute more than one process at the same time. This will increase the throughput of the system.

Spooling: Spooling is an acronym for simultaneous peripheral operations on line. Spooling refers to putting data of various I/O jobs in a buffer. This buffer is a special area in memory or hard disk which is accessible to I/O devices.

Booting: When the computer starts, the operating system is first loaded (as it is essential for running all other programs), this process is known as booting.

NICNIC stands for network interface card. NIC is a hardware component used to connect a computer with another computer onto a network.

  • Wireless NIC: The wireless NIC contains the antenna to obtain the connection over the wireless network. For example, laptop computer contains the wireless NIC.
  • Wired NIC: The Wired NIC is present inside the motherboard. Cables and connectors are used with wired NIC to transfer data.

Types of Virus

Following are the major types of computer virus −


This is a computer program that replicates itself at a swift pace. Unlike a computer virus, it is self-contained and hence does not need to be part of another program to propagate itself.

Trojan Horse

A Trojan Horse is also a sort of destructive program that remains disguised in a normal software program. It is not exactly a virus, as it cannot replicate itself. However, there is possibility that virus program may remain concealed in the Trojan Horse.


It is similar to Trojan Horse, but Logic bombs have some specialty; these include a timing device and hence it will go off only at a particular date and time.

Technologies related to virus

Computer worms "are self-replicating programs that spread with no human intervention after they are started." In contrast, "viruses are also self-replicating programs, but usually require some action on the part of the user to spread inadvertently to other programs or systems."

Unlike computer viruses and worms, Trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves. Trojans may allow an attacker to access users' personal information such as banking information, passwords, or personal identity. It can also delete a user's files or infect other devices connected to the network. Ransomware attacks are often carried out using a Trojan. After it is activated, it can achieve any number of attacks on the host, from irritating the user (popping up windows or changing desktops) to damaging the host (deleting files, stealing data, or activating and spreading other malware, such as viruses).

Zombie is a computer connected to the Internet that has been compromised by a hacker, computer virus or Trojan horse program and can be used to perform malicious tasks of one sort or another under remote direction.




  • Alt + F File menu options in current program
  • Alt + E Edit options in current program
  • Ctrl +A Select all text
  • Ctrl + F Find
  • Ctrl +X Cut selected item
  • Shift + Del Delete permanently
  • Ctrl + C Copy selected item
  • Ctrl + Insert Copy selected item
  • Ctrl + V Paste
  • Shift + Insert Paste
  • Home Go to beginning of current line
  • Ctrl + Home Go to beginning of document
  • End Go to end of current line
  • Ctrl + End Go to end of document


  • Ctrl+0 Toggles 6pts of spacing before a paragraph.
  • Ctrl+D Open the font preferences window.
  • Ctrl+E Aligns the line or selected text to the center of the screen.
  • Ctrl+J Aligns the selected text or line to justify the screen.
  • Ctrl+K Insert a hyperlink.
  • Ctrl+L Aligns the line or selected text to the left of the screen.
  • Ctrl+M Indent the paragraph.
  • Ctrl+N Opens new, blank document window.
  • Ctrl+O Opens the dialog box or page for selecting a file to open.
  • Ctrl+P Open the print window.
  • Ctrl+R Aligns the line or selected text to the right of the screen.
  • Ctrl+S Save the open document. Like Shift+F12.
  • Alt, F, A Save the document under a different file name.


Abbreviations in Computer Fundamentals

  • ALGOL – Algorithmic Language
  • AAC - Advanced Audio Coding
  • AMOLED – Active-Matrix Organic Light- Emitting Diode
  • AMD – Advanced Micro Devices
  • AVI – Audio Video Interleaved
  • ARPANET- Advanced Research Projects Agency Network
  • BASIC - Beginner’s All purpose Symbolic Instruction Code
  • BHTML - Broadcast Hyper Text Markup Language
  • BMP – Bitmap
  • COBOL – Common Business Oriented Language
  • DVDR – DVD Recordable
  • DVR – Digital Video Recorder
  • EBCDIC – Extended Binary Coded Decimal Interchange Code
  • ENIAC - Electronic Numerical Integrator and Computer
  • EDI - Electronic Data Interchange
  • GPRS - General Packet Radio Service
  • Gb - Gigabit
  • GB - Gigabyte
  • GIGO - Garbage in Garbage Out
  • HDMI - High Definition Multimedia Interface
  • HVD- Holographic Versatile Disc
  • INTEL - Integrated Electronics
  • ICANN - Internet Corporation of Assign Names &Numbers
  • ISDN - Integrated Servers Digital Network
  • ISO- International Standard Organization/
  • JPEG - Joint Photographic Expert Group.
  • MIPS – Million Instructions Per Second
  • MIDI - Musical Instrument Digital Interface
  • NAT - Network Address Translation
  • PDA - Personal Digital Assistant.
  • PNG - Portable Network Graphics
  • PSTN – Public Switched Telephone Network
  • PING – Packet Internet Gopher
  • PCB - Printed Circuit Board RIP – Routing Information Protocol
  • RTF – Rich Text Format
  • RARP - Reverse Address Resolution Protocol
  • SIM – Subscriber Identification Module
  • SMPS - Switch Mode Power Supply
  • SFTP Secure File Transfer Protocol
  • SSH - Secure Shell
  • SIP - Session Initiation Protocol
  • SAN -Storage Area Network
  • VGA – Video Graphics Array
  • WORM – Write Once Read Many
  • WPA    Wi-Fi Protected Access
  • WEP    Wired Equivalent Privacy
  • VLSM  Variable-length subnet masking
  • UTP     Unshielded twisted pair
  • TOFU  Trust On First Use

  • TIA      Telecommunications Industry Alliance
  • TFTP    Trivial File Transfer Protocol
  • STP      Spanning Tree Protocol
  • SSID    Service set identifier (Wi-Fi)
  • SNA     Systems Network Architecture (IBM)
  • SLIP     Serial Line Internet Protocol
  • SDN     Software Defined Networking
  • PTT      Public Telephone and Telegraph
  • PPTP    Point-to-Point Tunneling Protocol
  • PAP     Password authentication protocol
  • MTU    Maximum Transmission Unit
  • MAM   Media access management
  • ITU-T  International Telecommunications Union
  • IETF    Internet Engineering Task Force
  • IEEE    Institute for Electrical and Electronic Engineers
  • FDDI   Fiber Distributed Data Interface
  • EIA      Electronics Industry Alliance
  • EHA    Ethernet Hardware Address
  • DMI     Desktop Management Interface
  • DTE     Data Terminal Equipment
  • CMOS  Complementary metal-oxide semiconductor
  • CIDR   Classless Inter-Domain Routing
  • ACL     Access control list
  • AGP Accelerated Graphic Port
  • PCI      Peripheral Component Interconnect
  • UNIVAC Universal Automatic Computer
  • ATX    Advanced Technology Extended
  • ENIAC Electronic Number Integrator and Calculator
  • EDSAC   Electronic Dialog Storage Automatic Computer
  • LSIC    Large Scale Integrated Circuit
  • PDA     Personal Digital Assistant
  • USSD   Unstructured Supplementary Service Data
  • BASIC Beginner All Purpose Symbolic Instruction Code


Binary Coded Decimal, or BCD, is another process for converting decimal numbers into their binary equivalents.

It is a form of binary encoding where each digit in a decimal number is represented in the form of bits.

This encoding can be done in either 4-bit or 8-bit (usually 4-bit is preferred).

ex; Convert (123)10 in BCD

From the truth table above,

1 -> 0001

2 -> 0010

3 -> 0011

thus, BCD becomes -> 0001 0010 0011


Alphanumeric codes

A binary digit or bit can represent only two symbols as it has only two states '0' or '1'. But this is not enough for communication between two computers because there we need many more symbols for communication. These symbols are required to represent 26 alphabets with capital and small letters, numbers from 0 to 9, punctuation marks and other symbols.

The alphanumeric codes are the codes that represent numbers and alphabetic characters. The following alphanumeric codes are very commonly used for the data representation.

  • American Standard Code for Information Interchange (ASCII).
  • Extended Binary Coded Decimal Interchange Code (EBCDIC).

 ASCII code is a 7-bit code whereas EBCDIC is an 8-bit code. ASCII code is more commonly used worldwide while EBCDIC is used primarily in large IBM computers.

ASCII stands for the "American Standard Code for Information Interchange". ASCII is a 7-bit character set containing 128 characters. It contains the numbers from 0-9, the upper and lower case English letters from A to Z, and some special characters. The character sets used in modern computers, in HTML, and on the Internet, are all based on ASCII.

We use 65 for A and 97 for a.

EBCDIC (Extended Binary Coded Decimal Interchange Code): It is a 8 bit code.


CPU (Central Processing Unit):

ALU (Arithmetic Logic Unit): When the control unit encounters an instruction that involves mathematical calculation or decision/logic, it passes the control to the second component, i.e., the arithmetic logic unit (ALU). The ALU includes a group of registers - memory locations built directly into the CPU - that are used to hold data that are being processed by the current instruction.

Memory or Storage Unit can store instructions, data, and intermediate results. This unit supplies information to other units of the computer when needed. It is also known as internal storage unit or the main memory or the primary storage or Random Access Memory (RAM).

Control Unit: This unit controls the operations of all parts of the computer but does not carry out any actual data processing operations.

Types of Software:

  • Freeware: Software which is completely costless. The producers of this software are either public institutions such as universities or developers who do it for personal interest or advertisement or private company who do it for dumping reasons.
  • Shareware: Software which is initially costless but after a certain period the user is asked to pay a fee or delete it. Or software which has two versions a free one, but incomplete or with advertisement banners and a complete advertisement free one for which the user must pay. The most common example is WinZip compression program.
  • Commercial: Software for which the user has to pay a license to use it . Common examples are Microsoft Windows operating system and Microsoft word.
  • Private: Software uniquely built, under payment for a specific customer to fit his need. Only the customer may use it.
  • Open Source: Software may be modified by anyone, sometimes under certain restrictions. Open source software is also freeware.
  • Proprietary: Software is distributed with the explicit with the explicit legal warning not to modify it and technically locked to prevent other developers to see or modify its source.

Important Terms 

RAM (Random Access Memory) is directly connected to the CPU. In the old days, this was usually in a few chips on a circuit board next to a CPU, but these days, there’s usually some RAM inside a CPU. Small embedded CPUs may have all the RAM they need inside, while large PC-type CPUs will usually have a specialized kind of RAM called cache, which is used to store recently used information in RAM that’s extremely fast, trading back and forth with the main system RAM.

Digitizer- It converts analog information into digital form. It is an input device.

A motherboard connects CPU, memory, hard drives, optical drives, video card, sound card, and other ports and expansion cards directly or via cables. It can be considered as the backbone of a computer.

Bridge: A bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol.

In first generation computer, relied on Machine language (lowest level programming language understood by computer) Examples: The UNIVAC and ENIAC computers.

In second generation computer: High-level programming language also developed at this time such as an early version of COBOL and FORTRAN.

Fifth Generation (present and beyond) Artificial Intelligence.

Unix is a multi user OS.

Archieve: It provides backup storage.

Bitmap: A method of storing a graphic image as a set of bits in a computer memory. To display the image on the screen, the computer converts the bits into pixels.

BUS: A bus is a set of wires that enables flow of data from one location of the computer to another.

CMOS: CMOS is an abbreviation for Complementary Metal-Oxide-Semiconductor. It is the battery powered chip that is situated on the Motherboard that retains system information such as date and time.

FAT: FAT is an acronym for File Allocation Table. It resembles a table of contents so that files can be located on a computer.

E-mail messages are usually encoded in American Standard Code for Information Interchange (ASCII) text.

A popular protocol for sending e-mail is Simple Mail Transfer Protocol (SMTP) and for receiving it is POP3.

Data is an input for computer. Information is an output from computer.


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