Computer Awareness | Questions & Answers | Notes
Introduction to Computers
Basic Computer Concepts
Definition of a Computer A computer is an electronic device that can be programmed to accept data (input), process it into useful information (output), and store it away (in a secondary storage device) for safekeeping or later reuse. The processing of input to output is directed by the software but performed by the hardware.
Algorithm: It is a finite sequence of instructions. Each instruction should be precise, unambiguous, and capable of being carried out by a machine in a finite time.
Flow Chart: An algorithm expressed in a graphical form.
Programming Language : A precise notation used to express algorithms.
Computer Program : An algorithm expressed in a programming language.
Input Unit : It is required to receive data and instructions into the computer. The keyboard and mouse of a computer are the most commonly used input devices.
Central Processing Unit (CPU): Most important part of a computer system. It interprets the instructions in the program and executes one by one. It consists of three major units.
1. Control Unit: It controls and directs the transfer of program instructions and data between various units.
2. Arithmetic and Logic Unit (ALU) : Performs arithmetic operations like (+,-,*,A,/), logical operations like (AND, OR, NOT) and relational operations like (<,>,<=,>=).
Registers : They are used to store instructions and data for further use.
3.Memory Unit: It is used to store the Programs and data.
Output Unit : It is used to print/display the results, which are stored in the memory unit. The printer and monitor are commonly attached output units.
Secondary stored devices : It is referred to floppy disks, magnetic disks, magnetic disks, magnetic tapes, hard disks, and compact disks etc., which are used to store information for future use.
Peripheral devices : The input unit, output unit and secondary storage devices are together know as Peripheral devices.
Buses : The components of a computer are connected by using buses. A bus is a collection of wire that carries electronic signals from one component to another.
Interface standards : The various input and output devices have a standard way of connecting to the CPU and Memory. These are called interface standards. .
Ports : The places where the standard interfaces are provided.
Bits : Data in computers are represented by two digits 0 and 1. These digits are called Binary digits or Bits.
Byte : A set of bits is called a byte and each byte stores one character. Normally each byte is of eight bits.
ASCII (American Standards Code for Information Interchange): These are the codes used to represent each character. The ASCII code includes codes for English alphabets both capitals and small alphabets(A, B,.. .,X, Y, Z and a, b, c,.. .,x, y, z), decimal digits(0,l,2,.. .,8,9), 32 special characters and codes for a number of symbols used to control the operation of a computer which are non-printable.
Binary numbers : Binary numbers are formed using the positional notation. Powers of 2 are used as weights in the binary number system. A decimal number can be converted into an equivalent binary number by dividing the number by 2 and storing the remainder as the least significant bit of the binary number.
Hexadecimal Numbers : The base of the hexadecimal system is 16 and the symbols used in this system are 0,1,2,4,5,6,7,8,9,A,B,C,D,E,F. Strings of 4 bits have an equivalent hexadecimal value. .
Parity Check Bit: Errors may occur while recording and reading data or when data is transmitted from one unit to another unit in a computer. Detection of a single error in the code for a character is possible by introducing an extra bit in its code. This bit, know as the parity check bit, is appended to the code.
Key Board : It is used to input letters, numbers, and commands from the user.
Mouse : Mouse is a small device held in hand and pushed along a flat surface. It can move the cursor in any direction. In a mouse a small ball is kept inside and the ball touches the pad through a hole at the bottom of the mouse. When the mouse is moved, the ball rolls. This movement of the ball is converted into electronic signals and sent to the computer. Mouse has a use in Windows and other Graphical User Interface (GUI) applications.
Magnetic :Ink Character Recognition (MICR) Here human readable characters are printed on documents such as cheque using special magnetic ink. The cheque can be read using a special input unit, which can recognize magnetic ink characters. This method eliminates the need to manually enter data from cheques into a floppy. Besides saving time, this method ensures accuracy of data entry and improves security.
Optical Mark Reading and Recognition (OMR): Here pre-printed forms are designed with boxes which can be marked with a dark pencil or ink. Such a document is read by a document reader, which transcribes the marks into electrical pulses which are transmitted to the computer. These documents are applicable in the areas where responses are one out of a small number of alternatives and the volume of data to be processed is large. Widely used in Objective type answer papers in examinations in which large number of candidates appear.
Optical Character Recognition (OCR): A device used to read an image, convert it into a set of 0’s and l’s and store it in the computer’s memory. The image may be hand-written document, a typed or a printed document or a picture.
Bar Coding: In this method, small bars of varying thickness and spacing are printed on packages, books, badges, tags etc., which are read by optical readers and converted to electrical pulses. The patterns of bars are unique and standardized.
Speech Recognition : It takes spoken words as its input, and converts them to a form that can be understood by a computer.
Monitor or Video Display Unit (VDU): It provides visual display of data. They are of different types and have different display capabilities.
1. Display capabilities are determined by a special circuit called the Adapter card. Some popular adapter cards
(a) Color Graphics Adapter (CGA)
(b) Enhanced Graphics Adapter (EGA)
(c) Video Graphics Arraÿ (VGA)
(d) Super Video Graphics Array (SVGA)
2. The smallest dot that can be displayed is called a pixel.
3. The number of pixels that can be displayed vertically and horizontally gives the maximum resolution of the monitor. The resolution of the monitor determines the quality of the display. The higher the resolution the better is the quality of the display.
Line printer : It prints a complete line at a time. It has printing speed varies from 150 lines to 2500 lines per minute with 96 to 160 character on a 15-inch line. Six to eight lines per vertical inch can be printed. Usually it supports 64 and 96 character sets of English letters. Two types of Line Printers are available.
1. Drum Printers : It consists of a cylindrical drum. The characters to be printed are embossed on its surface
2. Chain Printers : It has a steel band on which the character sets are embossed.
Serial Printers : It prints one character at a time, with the print head moving across a line. They are similar to typewriters. They are normally slow (30 to 300 character per second)
Dot matrix printers: Here a character to be printed is made up of a finite number of dots Many dot matrix printers are bi-directional, i.e., they print form left to right as well as from right to left on return. This enhances the speed of printing. The printing speed is around 300 characters per second.
Inkjet Printer: It consists of a print head, which has number of nozzles. Individual nozzles can be heated very rapidly by an integrated circuit resistor. When the resistor heats up, the ink near it vaporizes and is ejected through the nozzle and makes a dot on paper placed near the head. Latest inkjet printers have multiple heads, on per color, which allows color printing. The printing speed is around 120 characters per second. As these printers do not have type head striking on a ribbon, they are known as non-impact printers.
Laser Printers : Here an electronically controlled laser beam traces out the desired character to be printed on a photoconductive drum. The drum attracts an ink toner on the exposed areas. This image is transferred to the paper, which comes in contact with the drum. These printers give excellent outputs and can print a variety of fonts. Since these printers do not have type head striking on a ribbon, they are known as non-impact printers.
Apart from printers, the other output devices are
• Drum Plotter
• Flat Bed Plotter
• Microfilm and Microfiche
• Graphic Display device (Digitizing Tablet)
• Speech Output Unit
1. A flip-flop made of electronic semiconductor devices is used to fabricate a memory cell. These memory cells organized as a Random Access Memory (RAM). Each cell has a capability to store one bit of information. A main memory or store of a computer is organized using a large number of cells. Each cell stores a binary digit.
2. A memory cell, which does not loose the bit stored in it when no power is supplied to the cell, is known as a
non-volatile cell. .
3. A word is a group of bits, which are stored and retrieved as a unit. A memory system is organized to store a number of words.
4. A Byte consists of 8 bits. A word may store one or more bytes.
5. The storage capacity of a memory is the number of bytes it can store.
6. The address of the location from where a word is to be retrieved or to be stored is entered in a Memory Address Register (MAR).
7. The data retrieved from memory or to be stored in memory are placed in a Memory Data Register (MDR).
8. The time taken to write a word is known as the Write time.
9. The time to retrieve information is called the Access time of the memory.
10. The time taken to access a word in a memory is independent of the address of the word and hence it is know as a Random Access Memory (RAM).
• The main memory used to store programs and data in a computer is a RAM.
11. A RAM may be fabricated with permanently stored information, which cannot be erased. Such a memory is called a Read Only Memory (ROM).
• For more specialized uses, a user can store his won special functions or programs in a ROM. Such ROM’s
are called Programmable ROM (PROM). .
12. A serial access memory is organized by arranging memory cells in a linear sequence.
• Information is retrieved or stored in such a memory by using a read/write head.
• Data is presented serially for writing and is retrieved serially during read.
Secondary / Auxiliary storage devices :
Magnetic surface recording devices used in computers as Hard disks, Floppy disks, CD-ROMs and Magnetic tapes.
1. Floppy Disk Drive (FDD): In this device, the medium used to record the data is called as floppy disk. It is a flexible circular disk of diameter 3.5 inches made of plastic coated with a magnetic material. This is housed in a square plastic jacket. Data recorded on a floppy disk is read and stored in a computer’s memory by a device called a floppy disk,is read and stored in a computer’s memory by a device called a floppy disk drive (FDD). A floppy disk is inserted in a slot of the FDD. Floppy Disks with various capacities are as follow:
• 51/4 drive- 360KB, 1.2MB (1 KB= 210 = 1024 bytes)
• 3I/2 drive-1.44 Mb, 2.88 MB (1MB= 220 bytes)
2. Compact Disk Drive (CDD): CD-ROM (Compact Disk Read Only Memory) used a laser beam to record and read data along spiral tracks on a 51/4 disk. A disk can store around 650 MB of information. CD-ROMs are normally used to store massive text data. Recently CD writers have come in the market. Using a CD writer, lot of information can be written on CD-ROM and stored for future reference.
3. Hard Disk Drive (HDD): Unlike a floppy disk that is flexible and removable, the hard disk used in the PC is permanently fixed. The data transfer rate between the CPU and hard disk is much higher as compared to the between the CPU and the floppy disk drive. The CPU can use the hard disk to load programs and data as well as to store data.
Application and System Software
Software : A set of programs associated with the operation of a computer is called software.
Hardware : The electronic circuits/ devices used in building the computer that executes the software is known as. the hardware of the computer.
Application Software : It is the set of programs necessary to carry out operations for a specified application.
System Software: These are general program written for the system, which provide the environment to facilitate writing of Application software.
Compiler : It is a translator system program used to translate a High-level language program into a Machine language program.
Assembler: It is another translator program used to translate an Assembly language program into a Machine language program.
Interpreter: It is also a translator system program used to translate a High level language program into a Machine language program, but it translates and executes line by line.
Loader: It is a system program used to store the machine language program into the memory of the computer.
Task-Oriented Software : Most users, whether at home or in business, are drawn to task-oriented software, sometimes called productivity software that can make their work faster.
Word Processing/Desktop Publishing: The most widely used personal computer software is word processing software. This software lets one create, edit, format, store, and print text and graphics in one document. Desktop publishing packages are usually better than word processing packages at meeting high-level publishing needs, especially when it comes to typesetting and color reproduction. Many magazines and newspapers today rely on desktop publishing software
Electronic Spreadsheets : Spreadsheets, made up of columns and rows, have been used as business tools for centuries A manual spreadsheet can be tedious to prepare and, when there are changes, a considerable amount of calculation may need to he redone. An electronic spreadsheet is still a spreadsheet, but the computer does the work. In particular, spreadsheet software automatically recalculates the results when a number is changed. This capability lets business people try different combinations of numbers and obtain the results quickly. One use Microsoft’s Excel spreadsheet application software.
Database Management: These software are used for database management.
Graphics : One use it in two ways: for doing original drawings, and for creating visual aids to project as a support to an oral presentation.
Machine language: The computers can execute a program written using binary digits only. This type of programs is called machine language programs. These programs written for execution in one computer cannot be used on another type of computer, i.e., the programs were machine dependent. At presenUcomputer users do not write programs using machine language.
Assembly Language: In assembly language mnemonic codes are used to develop program for problem solving. Assembly language is designed mainly to replace each machine code with and understandable mnemonic code. To execute an assembly language program it should first be translates into an equivalent machine language program. Writing and understanding programs in assembly language is easier than that of machine ian^ua^e. The programs written in assembly language are machine dependent.
High Level Languages: High level languages are developed to allow application programs, which are machine independent. High level language permits the user to use understandable codes using the language structure. In order to execute a high-level language program, it should be translated into a machine language either using a compiler or interpreter.
1. Earlier high level languages commonly used are FORTRAN (FORmula TRANslation), BASIC (Beginner’s All-purpose Symbolic Instruction Code), COBOL (COmmon Business Oriented Language).
2. Lately developed programming language Visual Foxpro, Visual Basic (VB), Visual C++ (VC++) are more popular among the software developers.
Classification of Computers
Computers come in sizes from tiny to monstrous, in both appearance and power. The size of a computer that a person or an organization needs depends on the computing requirements.
Supercomputers : The mightiest computers-and, of course, the most expensive-are known as supercomputers. Supercomputers process billions of instructions per second. One uses supercomputers for tasks that require mammoth data manipulation, such as worldwide weather forecasting and weapons research.
Mainframes : In the jargon of the computer trade, large computers are called mainframes. Mainframes are capable of processing data at very high speeds-millions of instructions per second-and have access to billions of characters of data. Their principal use of it is for processing vast amounts of data quickly, some of the obvious customers are banks, insurance companies, and manufacturers.
Personal Computers : Personal computers are often called PCs. A PC usually comes with a tower that holds the main circuit boards and disk drives of the computer, and a collection of peripherals, such as a keyboard, mouse, and monitor. The term “PC” often means machines that are compatible to IBM other than a Macintosh.
Personal Computers (PC) and MAC: A PC is based on a microprocessor originally made by the Intel Company (Intel’s Pentium) with other companies such as AMD. The computers made by Macintoshes which uses, PowerPC processor, made by Motorola are referred as Mac. Also, the operating system software that runs these two kinds of computers is different. PCs usually use an Operating System made by Microsoft, i.e., Windows. Macintoshes use operating system, called Mac OS, made by Apple.
Notebook Computers : A computer that fits in a briefcase?. Notebook computers, also known as Laptop computers, are portable and popular with travelers who need a computer that can go with them. Most notebooks -accept diskettes or network connections, so it is easy to move data from one computer to another.
Computers and Communications
Modem : A device used to transfer data from one computer to another using the telephone lines. A modem converts the strings of Os and Is into electrical signals which can be transferred over the telephone lines. Both the receiving and the transmitting computer have a telephone connection and a modem.
(a) External modem is connected to the computer like a typical input or an output device.
(b) Internal modem is fitted into the circuitry related to the CPU and Memory.
Local Area Network (LAN) : A interconnection of computers which are within the same building or nearby locations forms a network of computers and this network is called a Local Area Network (LAN). A LAN permits sharing of data files, computing resources and peripherals.
Wide Area Network (WAN) : A interconnection of computers located in far away locations using telecommunication system.
Internet: Computer networks located in different Organizations can communicate with each other through a facility know as Internet. Internet is a world wide computer network, which interconnects computer networks across countries. The Internet facilitates electronic mail (email), file-transfer between any two computers and remote access to a computer connected in the internet.
THE GENERATIONS OF COMPUTER
The Generations of Computer: A generation refers to the state of improvement in the development of a product. It also is used for major state of different advancements/achievements of computer technology. With each new generation, the circuitry has gotten smaller and more advanced than the previous generation before it. As a result of the miniaturization, speed, power, and memory of computers have proportionally increased. The time span of era of computer generations may vary in different prospects.
The First Generation : 1946-1958 (The Vacuum Tube Years)
1. The first generation computers were huge, slow, expensive, and often undependable and used Vacuum tubes in CPU’s.
2. In 1946 two Americans, Presper Eckert, and John Mauchly built the ENIAC electronic computer which used vacuum tubes instead of the mechanical switches of the Mark I. The ENIAC used thousands of vacuum tubes, which took up a lot of space and gave off a great deal of heat.
• The ENIAC led to other vacuum tube type computers like the EDVAC (Electronic Discrete Variable Automatic Computer) and the UNIVAC I (UNIVersal Automatic Computer-1).
First generation computers relied on machine language to perform operations, and they could only solve one problem at a time.Input was based on punched cards and paper tape, and output was displayed on printouts.
The Second Generation : 1959-1964 (The Era of the Transistor)
1. Transistors replaced vacuum tubes and ushered in the second generation of computers.
2. In 1947 three scientists, John Bardeen, William Shockley, and Walter Brattain working at AT&T’s Bell Labs invented transistor which functions like a vacuum tube.
3. The transistor was faster, more reliable, smaller, and much cheaper to build than a vacuum tube.
• These transistors were made of solid material, some of which is silicon.
• Transistors were found to conduct electricity faster and better than vacuum tubes. They were also much smaller and gave off virtually no heat compared to vacuum tubes. Second-generation computers still relied on punched cards for input and printouts for output.
4. Second-generation computers moved from cryptic binary machine language to symbolic, or assembly, languages, which allowed programmers to specify instructions in words.
5. High-level programming languages were also being developed at this time, such as early versions of COBOL and FORTRAN.
6. These were also the first computers that stored their instructions in their memory, which moved from a magnetic drum to magnetic core technology.
The Third Generation : 1965-1970 (Integrated Circuits – Miniaturizing the Computer)
1. Integrated Circuits (IC) are introduced that have started replacing transistors.
2. The integrated circuit, or as it is sometimes referred to as semiconductor chip, packs a huge number of transistors onto a single wafer of silicon. Placing such large numbers of transistors on a single chip vastly increased the power of a single computer.
3. Most electronic devices today use some form of integrated circuits placed on printed circuit boards— thin pieces of bakelile or fiberglass that have electrical connections etched onto them — sometimes called a mother board. These third generation computers could carry out instructions in billionths of a second.
4. Instead of punched cards and printouts, users interacted with third generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program that monitored the memory.
5. Computers for the first time became accessible to a mass audience because they were smaller and cheaper than their predecessors.
The Fourth Generation: 1971-Today (The Microprocessor)
1. This generation can be characterized by both the jump to monolithic integrated circuits (millions of transistors put onto one integrated circuit chip) and the invention of the microprocessor (a single chip that could do all the processing of a full-scale computer).
2. bv putting millions of transistors onto one single chip more calculation and faster speeds could be reached by computers.
• Ted Hoff, employed by Intel invented a chip the size of a pencil eraser that could do all the computing and logic work of a computer.
• The Intel 4004 chip, developed in 1971, located all the components of the computer – from the central processing unit and memory to input/output controls – on a single chip.
3. Microprocessors moved out of the realm of desktop computers and into many areas of life as more and more everyday products began to use microprocessors.
• In 1981 IBM introduced its first computer for the home user
• In 1984 Apple introduced the Macintosh.
4. As these small computers became more powerful, they could be linked together to form networks, which eventually led to the development of the Internet.
5. Fourth generation computers also saw the development of GUIs, the mouse and handheld devices.
Fifth Generation – Present and Beyond: Artificial Intelligence:
1. Fifth generation computing devices, based on artificial intelligence, are still in development, though there are some applications, such as voice recognition, that are being used today.
2. The use of parallel processing and superconductors is helping to make artificial intelligence a reality.
3. Quan tu m computation and molecular and nanotechnology will radically change the face of computers in years to come.
4. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.