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Friday, 27 August 2010


Introduction to Computers

            Today Information Technology is changing at a lightening, speed, by ripping of age-old beliefs.  In to-days world, accessing distribution, storing and retrieving of information has become part of ones life.  In this era of changing technologies computers are playing hetero-centric role.
Mainly computer age has been divided into three ages

The Dark Ages (500 BC – 1890 AD)
The Middle Ages (1890 – 1944) and
The Modern Age (1944 onwards)

            As early as 500 BC, the ancient Egyptians were using the bead-and-wire abacus to add and subtract large numbers.  In 1642, Blaise Pascal of France invented a machine he called the “Pascaline” that could add, subtract, carry between digits and calculate the exchange rate of national currencies.  In 1674, Gottfried Wilhelm Leibnitz of Germany created a machine that could add, subtract, multiply and divide automatically.  These machines preceded the discovery of electricity by over one hundred years!
            The first computers were the size of whole rooms and used vaccum-tube, electronic technology and used in world War Two.  These computers were difficult to maintain and extremely slow. 
            In 1970s, microcomputers for consumers began to appear.  Radio Shack, Commodo, Apple Computer Inc. and Texas Instruments introduced the personal computer.  In 1981, IBM released the IBM PC (personal computer).  Through the 1980s and 1990s, Microsoft and Intel released next generations of computer chips and operating system software.
            The Internet is the next great computer frontier.  The modern PC has roots that go back to the USA in the 1940s.  Computer hardware down in five primary parts:

Ø       CPU (Central Processing Unit)
Ø       Input
Ø       Output
Ø       Working memory
Ø       Permanent memory

The first three computer generations are linked to the development of three technologies.
o        The Vaccum tube
o        The Transistor and
o        The Integrated Circuit

The First Generation (1951-1958): Thousands of such tubes were required; they generated a great deal of heat, causing many problems in temperature regulation and climate control.  The tubes were subjected to frequent burnout.  Machine language (0s and 1s) was used for programming.  This made programming difficult and time consuming.

The Second Generation (1959-1969): Transistor, that transferred electric signals across a resistor, were much smaller than vacuum tubes, needed no warm up time, consumed less energy and were faster and more reliable.  It moves from machine language to assembly language.  Assembly language used abbreviations for instructions rather than numbers Eg: ADD for addition.

The Third Generation (1965-1970): An Integrated circuit (IC) is a complete electronic circuit on a small chip of Silicon.  It is less than 1/8 inch square and contains thousands or millions of electronic components.  In 1965, IC began to replace transistors.  ICs are made of Silicon, which is a semi conductor.  Reliability, compactness and low cost are its characteristics.

The Fourth Generation (1971-Present day):  This generation large scale integration (LSI) of circuitry was introduced. Large scale networking of computers began.

The Fifth Generation (Onwards):  Fifth generation was coined by the Japanese to describe the powerful, intelligent computers they wanted.  Several research fields related to computer intelligence, artificial intelligence, expert systems, natural language and neural networks.

Characteristics of a Computer

Speed: The processing speed essential to our fast-paced society.  A computer speed is generally expressed in Megahertz (MHz), millions of machine cycles per second.

Accuracy: Results given by computer are accurate and consistent.  Mistakes attributed to computers are human errors.

Storage and Retrieval: It can store tremendous amounts of data, which can be located and retrieved sufficiently.  A typical mainframe computer system will have many billions of characters stored and available for instant recall.

Reliability: They are extremely reliable for operation without failure.

Reliability of Computer: Serviceable time is the total time during which a computer can operate normally, including time when the computer is idle.  Down time is the time when a computer is inoperable due to machine fault.

Flexibility:  It provides fast access to information, process date, text, signals and generates reports in no time.

Classification of computer
They can be classified in two basic categories.

Analog Computers:  It use signals as output

Digital Computers:  It accepts digits as input on (high) and off (low) voltage state of electricity.  0 and 1 as low and high.  Digital watch is an example of this.

Hybrid Computers:  These computers which adopt the best qualities of both analog and digital systems.  They are used for automation of various complicated physical process and machines.

Types of Computers

Super Computers
            They are still the size of rooms.  The most expensive and are used for complex scientific calculations, space missions and military purposes.  It is the most powerful category of computers for processing huge quantities of date at very high speeds.

Ø       Provides greater computing capacity, grater storage
Ø       Offers better accuracy & reliability because of parallel processing
Ø       Has a word length of 64 to 96 bits
Ø       Has speed varying from 400-10000 MFLOPS (Millions of Floating Point Operations per Second)
Ø       Has RAM in the order of Gigabytes.

            Areas of application: To solve milti-variable mathematical problems occurring in Aero-dynamics, Meteorology, Seismology and Entertainment/Advertisement Industry.
            Example: CRAY-3/CYBER 205/PARAM (INDIA)

Mainframe Computer

            The largest type of computer in common use in the Mainframe Computer.  They are designed to handle tremendous amounts of input, output and storage.  It is used as a Database server.
Ø       Word length between 48 and 64 bits
Ø       RAM in the order of Megabytes/Gigabytes
Ø       Processing speed varying from 30 to 100 MIPS (Million Instructions per Second)

            Areas of Application: Banking sectors, Airline & Railway reservations, Insurance companies and Research organizations.
            Example: IBM-4300, IBM-308, IBM-3090/HP-9000/VAX-8842

Mini Computer

            Mini computer is better described whose capabilities lie some where between that of mainframe and personal computers.
Ø       Word length of 32 bit
Ø       RAM upto 256 MB
Ø       Speed varying from 10 to 30 MIPS

            Areas of Application: Payroll preparation, scientific computations and engineering design
            Example: DEC/HP/IBM

Micro Computer/Personal Computer

            The personal computers generally refer to the small computers that are commonly found in offices, classroom and homes.  A desktop model is the most common of PCs and is small enough to fit on a desk.
Ø       Word length of 16 to 32 bit
Ø       RAM up to 256 MB
Ø       Speed measured in MHz/GHz instead of MIPS
Ø       Speed varying from 550 MHz to 2 GHz

            Areas of Application: Home/small office applications
            Example: APPLE/IBM/COMPAQ/HP

Laptop/Notebook Computer

            Among the portable computers, a notebook computer approximates the size of an 8.5” X 11” notebook and it can easily fit inside a briefcase. It is a Mobile Computer, roughly the size of a notebook with specifications almost same as Personal Computer.

Ø       Can be used while traveling
Ø       Accessories like tables etc. not required
Ø       Does same work as Personal computer

Manufacturers: IBM- Notebook, DELL, Compaq etc.

Personal digital assistants (PDAs) are the smallest of portable computers.  They are also called Palmtops.  They are much less powerful than a notebook or desktop, generally used for displaying important telephone numbers and addresses or keeping track of dates and agendas.  They can be connected to larger computers to exchange data.

Workstations are used in Hollywood to create the special effects that we see in films.

Network Servers
They are computers that run office network and other mid-sized systems.  The present day PCs are having the capabilities of mainframes or minicomputers.

Computer and its components

Computer is a composition of both hardware and software.  Hardware is physical identification of the components and software is the set of instructions that makes the components to work.  At first we deal with the hardware which is a physical substance.

            Hardware is a collection of various physical components.  Software is a set of instructions, which makes the components to respond or execute the given task.  Software like our brain, issues specific task-based instruction to drive the hardware components.  First of all, The Motherboard, which will be housed in a cabinet, is the central piece that all the other components connect (or eventually connect) to.

The mother board consists of the following components:

            The processor speed is the deciding factor, how faster a computer is?  Processor speed is generally expressed in Megahertz (MHz), millions of machine cycles per second.

Output devices

The Monitor
            The monitor, known as video display unit, is used for displaying the needful information received from CPU.  The CPU after processing the data sends the information to the video adapter.  The video adapter converts the signals into understandable information and displays on the video terminal. Monitors are categorized into monochrome and colour.

            The printers are used for outputting the required information from the computer, known as soft copy, on to a media or paper, known as hard copy.  There are printers with various capabilities.  They are categorized into Impact and non-impact.

Impact printers works on the basic principle of typewriter.  Each character printed will be hit against a ribbon on to a paper to create the impression.  Impact printers are Dot matrix printers, line printers etc.  The disadvantage is that they give a low quality print outputs.  They are cheaper.

Dot matrix printer: In DMP, the print head physically “hits” the paper through the ribbon and produces text (or images) by combinations of dots; hence the name dot matrix printer.  Its speed is measured in characters per second (CPS).

Line printer:  It is generally used with large computer systems.  They are high speed printers.  The speed ranging is about 100 to 3800 lines per minutes.

            Non impact printers are which use the electro static or ink spray technology for printing.  The output quality of both graphic and text is better when compared to impact printers.  Laser printers produce a higher and sharp image quality.  These printers are expensive in maintenance.  Some of the non-impact printers are inkjet printers, laser printers etc.

Laser printer: It produces faster and noise less high quality prints that one normally finds in publishing houses.

Ink-jet printer: An ink-jet printer creates an image directly on paper by spraying ink through as many as 64 tiny nozzles. The quality of inl-jet images is still high.  Providing print resolution of aroung 360 or more dots per inch.

Plotter: Plotters are designed to produce large drawings or images, such as construction plans for buildings or blueprints for mechanical objects.  It has a flat bed, an array of different coloured pens in a clip rack and a robotic arm to draw with coloured pens.  The instructions that a plotter receives from a computer consist of a colour, the plotter picks up the appropriate pen through its arm, positions it at the beginning co-ordinates and draws curves by creating a sequence of very shot straight lines.

Input devices

Floppy drives:  The floppy drive is one of the basic and primary storage device.  It is a magnetic storage media.  The floppy which is of the size 305”, holds the date to the size of 1.44Mb.  Data is recorded in the magnetized states of particles of iron oxides evenly placed upon concentric circles known as tracks.  Tracks are further divided into sectors.

Hard disk:  It is a non-removable magnetic storage device.  It contains a stack of magnetic wafer like metal plates that spin on a spindle.  The size of HDD will be in Mbs/Gbs.

CD-Rom (Compact disk read only media)

            CD start as round wafers made from a polycarbonate substrate, measuring 120mm (about 4.75 inches) in diameter and about 1.2mm in thickness, which is less than 1/20th of an inch.  The first step is the

production of a master. The data to be recorded is created as an image of ones and zeros.  The image is etched into the master CD using a relatively high-power laser.  Using special data encoding techniques that use microscopic pits to represent the data.  The actual CDs are produced by pressing them with the master stamp.  This creates a duplicate of the original master.  The entire disk is coated with a thin layer of aluminum which makes the disk shine.
            The data surface of the CD is actually the top of the disk. The player reads the CD from the bottom by focusing the laser through the 1.2mm thickness of the CD’s substrate.  The bottom of the disk can have small scratches.  Scratches on the top of the disk can actually remove strips of the reflective aluminum coating, leaving the disk immediately unusable.

            They are not too sensitive to heat but will warp if left to bake in direct sunlight on a hot summer’s day.  CD media should always be cared.  The use of caddies or jewel cases will protect them; in general, the less handling, the better.  In general the capacity of the CD ROM is 650MB.

            CD ROMs are used for one time writing.  It is also available which can be reused for a limited no. of times approximately 10 times.

Keyboard:  It is the most common input device.  Several kinds of keyboards are available.  The most commonly used keyboard is the QWERTY board.  At present we have remote keyboards and keyboards with Internet linkup buttons.

Mouse:  It is a device having two or three buttons.  These buttons are used for selection or possible events of a graphic object.  The mouse is an electro-mechanical device.  It uses a magnetically coated ball, to detect the movement of the mouse across a flat surface, usually a desktop.  Some mouse, which works on the basis of reflection of light.  It is not a substitute, but an add-on to the key board.

Scanner:  It translates printed images into an electronic format that can be stored in a computer’s memory.

Magnetic Ink Character Reader (MICR):  It is a recording of information on document by means of magnetized ink characters using machines.

Now let us understand what software is.

Software is a set of instructions, which are required to accomplish a task or to run a component of hardware.  It can also be termed as a program.  The capability of the computer largely depends on the software component.

            A computer can be compared to a human being, like, human body can be considered as hardware and oxygen a source of life by which instructions will be given to various parts of the body can be considered as software.

            A simple architecture of the computer is given below, which shows how input, CPU and output devise are integrated.

Central Processing Unit
            It is a single component that does the actual computing.  This is the CPU.  The CPU is a single “chip” on the order of one square inch in size.  The job of the CPU is to execute programs.

            A computer is built to carry out instructions that are written in a very simple type of language called machine language.  Each type of computer has its own machine language.  When the CPU executes a program, that program is stored in the computer’s main memory (also called RAM or Random Access Memory).  Main memory consists of a sequence of locations.  These locations are numbered and the sequence number of a location is called its address.  An address provides a way of picking out one particular piece of information from among the millions stored in memory.  When the CPU needs to access the program instruction or data in a particular location, it sends the address of that information as a signal to the memory; the memory responds by sending back the data contained in the specified location.  The CPU can also store information in memory by specifying the information to be stored and the address of the location where it is to be stored.

            The CPU executes a program that is stored as a sequence of machine language instructions in main memory.

Machine language instructions are expressed as binary numbers.  A binary number is made up of just two possible digits, 0 and 1.  A machine language instruction is just a sequence of 0’s and 1’s.  Each particular sequence encodes some particular sequence encodes some particular instruction.  Turn the switch on to represent a one; turn it off to represent and zero.  Machine language instructions are stored in memory as patterns of switches turned on or off.  The CPU is built to respond to this pattern by executing the instruction it encodes; it does this simply because of the way all the other switches in the CPU are wired together.

            It coordinates and controls the activities of input, output and storage devices, and performs all the arithmetic and logical processes to be applied to data.  All data to be processed must first be loaded into this unit.

            The complex procedure that transforms raw input data into useful information for output is called processing.  The CPU consists of:
Ø       Memory (Primary storage)
Ø       Control unit and
Ø       Arithmetic Logic unit (ALU)

Different types of memory and usage

            The CPU does not have sufficient storage space.  Therefore, the control unit stores data and instructions received from input devices into primary memory called Random Access Memory (RAM).  RAM holds information only while the computer is on.  RAM is often referred to as temporary memory.
            Some of the date and instructions remain permanently stored in the memory is called Read Only Memory (ROM). A computer needs ROM, so that it knows what to do when the power is first turned on.  ROM contains a set of start up instructions to see that the rest of memory is functioning properly.  This memory never gets lost; it is sometimes referred to as permanent or non-volatile memory.

            The performance of a computer depends upon the data transfer rate between CPU and memory.  Faster the data transfer rate, costlier the computer.  A Cache memory that acts as a buffer between primary memory and CPU.  Present day computers, cache is a part of the microprocessor itself.

            The Cache speeds up processing, by storing frequently used data or instructions in its high speed memory.  Whenever the CPU requests information from RAM, the cache controller intercepts the request and searches its own memory for the requested information.  If the information is there, the CPU retrieves the required data from the memory (RAM) and also sends a copy back to the cache.  The next time the CPU needs the same information; the cache finds that information and quickly sends it to the CPU leaving RAM out of the loop.

Understanding the storage capacity
            One of the main uses of computer is for storing and retrieving information.  That information, be it text, numbers, of graphics, is stored on disks.  More the disk storage capacity a computer has, more the information it can store.  The amount of the information a computer can store is measured in bytes.  It takes 6 bytes to stores the word “svpnpa”, and 13 bytes to store the words “police academy”.

            A kilobyte, often abbreviated as K or KB is about 1024 bytes.  A megabyte as MG is about 1024 kil bytes.  A gigabyte as GB is about 1024 megabytes.  All modern computers use a hard disk to store information.  The storage capacity of a hard disk is measured in megabytes/gigabytes.

            The control unit manages all the computer resources and coordinates all the computer’s activities.  It contains the basic instructions for executing of programs.  The control unit can be thought of as a traffic cop, directing the flow of data around the CPU and around the computer.

            When the control unit encounters an instruction that involves mathematical calculation or decision/logic, it passes the control to the arithmetic logic unit (ALU).

Various types of memories
  1. Random Access Memory (RAM): When the power is not there the RAM will be empty.  Whenever new program is executed the contents of the previous data will be lost.

  1. Read only Memory (ROM): Certain necessary repetitive or fixed instructions to run the system are always required by the computer.

  1. Secondary memory: Floppy, hard disk, magnetic tapes etc are some of the secondary memory devices.

  1. Cache memory: This is a high speed memory, which is used to store portion of a program from main memory temporarily.  The cache memory is very expensive but it is very fast.  The data is transferred automatically.

How the data is communicated between different units?

            There are different units ALU, MU and control unit.  Data is communicated between these units by means of three buses.  They are 1. Control bus 2. Address bus 3. Data bus.
These are electrical paths for the data to flow from point to point in a circuit.

Control bus: It is the path for all controlling and timing function sent by the control unit to other units of the CPU.

Address bus: It is the path used for locating the address of the memory location where the next instruction to be executed or the next piece of data.

Data bus: This is the path on which actual data transfer takes place.

Computer registers: Registers are special temporary storage location, which are within the central processing unit.  They are very fast.  They accept store transfer data and instructions, which are in immediate use.  The instructions being executed is retrieved by CPU from the main memory and stored in registers.  Registers hold only 8 bits there are other type of registers that can hold 16 or 32 bits.


System Software:  It controls all processing activities.  The resources and the power of the computer are used in most efficient manner.  It basically serves 2 major purposes.  1. It controls the execution of program on the computer.  2. It aids the development of software.  The system software consists following software:

Operating system software: The software that does all the interrupt handling and the communication with the user and with hardware devices is called the operating system.  The operating system is the basic, essential software without which a computer would not be able to function.  Word processors and World Wide Web browsers are dependent upon the operating system.  Common operating systems include UNIX, DOS, Windows and the Macintosh OS.

            They can be classified as single user and multi user depending on the number of users working on it at a given point of time. DOS is a single user OS and UNIX, Windows-NT are the examples of multi user software.

Language Processor Software: The data will be converted in a machine language, which the system can understand.  The software, which makes this conversion possible and increases the productivity of the programmer are called translators.  There are 3 basic types of translators.  They are 1. Compilers 2. Interpreters 3. Assembler.


Pre-written application software is designed by a group of people to be used by others.  The most commonly available prewritten application software is
  1. Word processing software
  2. Database management software
  3. Communication software

User written software is usually for a special task of an organization or for a specific application.

Programming Languages

Languages specially invented for the purpose of instructing computers to perform various operations in the correct sequence.  Programming languages are called “lower” or “higher” depending on how close they are

to the language, the computer itself uses (0s and 1s) or to the language people use (more English like – High)

Machine language (First Generation)
            Computers recognize and operate in binary numbers.  This machine language is the lowest level of language which represents data and program instructions as 1s and 0s.

Assembly Language (Second Generation)
            The symbolic instructions are translated into binary coded instructions by a special program called on Assembler.  An assembler translates the symbols; this type of symbolic program is referred to as an assembly language program.

High Level Language (Third Generation)
            Assembly language is specific to a given machine, are not transferable from one machine to another.  To overcome, this limitation, languages such as BASIC (Beginners All-purpose Symbolic Instruction Code), FORTRAN (FORmula TRANslation) have been devised.  These languages are called high-level languages.  It must be translated into machine language before it can be executed.

Fourth Generation Languages (4GLs)
The fourth generation language is any high level language designed to enable users who are not trained programmers.  The characteristics of 4GL include English-like instructions, limited mathematical manipulation of data, automatic report formatting, sequencing and record selection by criteria.

Natural Languages

            Fifth generation languages are often called natural languages because of their resemblance to the “natural” spoken English language.  The logic behind a natural language is that the programmer or user needs little or training.  The use of a natural language to access a knowledge base is called knowledge-based system.  All modern computers use multi tasking to perform several tasks at one.  Some computers can be used by several people at once.  This application of multi tasking is called time sharing.  For eg. The user might be typing a paper while a clock is continuously displaying the time and a file is being downloaded over the network.  Each of the individual tasks that the CPU is working on is called a thread.  Only one thread can actually be executed by a CPU.

How computer understand data?

            Computer can only understand 0, 1 machine language, which is nothing but the electronic pulse.  Each pulse will have a universal standard code, called ASCII (American Standard Code for Information Interchange)

Decimal number system: The digit of this number system starts from 0 to 9.  To use this number system by the computer, it requires 10 different types of electronic pulses, which makes the operations complicated.

Binary number system: The advantage of this number system is that it has two distinct digits to represent the electronic pulse ‘off’ and ‘on’.  The advantages of this number system is

  1. Hardware electronic circuit is simple
  2. Cost of the circuit design comes down
  3. Computers identify digital signals, which represent either high or low voltage.

Word Processing
Word processing software enables users to display typed information on a screen and manipulate, edit and delete it without wasting paper whenever changes are made.

They are indispensable for working with numbers.  Information is displayed in table form on the screen, like an accounting ledger.  Users can program calculation instructions right into the table.  The spreadsheet software performs these calculations automatically.

Databases allow us to gather and analyze large amounts of information instantaneously.

Computer-aided Drawing
Computer aided drawing (CAD) programs are used by Engineers and architects to produce plans of objects or buildings that can be viewed from any perspective and edited on screen without having to produce blueprints.

Computers have made the world a smaller place with their ability to move information instantly over large distances.  It manages broadcast and telephone networks all over the planet.  The Internet enables people to sent E-mail anywhere in the world at very low cost.

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