Computer fundamentals


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Computer fundamentals

  1. 1. Shree M. & N. Virani Science College Computer Fundamentals By Milan Kothari“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 1
  2. 2. Shree M. & N. Virani Science CollegeCOMPUTER CONCEPTNeed for Computer literacyInvention of computers has brought a major technological revolution. Computers have moved into society sorapidly and so completely that we need basic computer skills to pursue our career goals and function effectivelyin society. In short, to live and work in a computerized society we should be computer literate.A mere knowledge of pressing the keys of keyboard and feeding data into the system is not only the objective ofbeing a computer literate. We need to understand some fundamental concepts about how computer systemswork and can be effectively used for general-purpose and special-purpose.It is important to know how to handle a computer system otherwise one cannot take the full advantage of thecomputers. Lack of knowledge causes several problems while using computers. Sometimes many peoplegenerate irrational fear of computers and this is termed as cyberphobia.Computer:It is an electronic device or a flexible machine, which can manipulate data. These manipulations may or may notbe mathematical. Or more accurately a computer may be defined as a device that operates upon data.Data can be anything like bio-data of various applicants when the computer is used for recruiting personnel. orthe marks obtained by candidates in a competitive exams such as medical entrance, engineering entrance, civilservice examination etc.Data comes in various shapes depending upon the type of computer application. A computer can store. processand retrieve data as and when required. Due to the fact that computers process data is so fundamental thatmany people have started calling it a data processor.Computers are so flexible that people feel comfortable and equally at home while using them. A computer isprogrammable. It means computer depends upon the program which is in use by it. No matter which program acomputer is using, the machine-itself performs only four basic operations.(a) Input: A computer accepts data that is provided by means of an input device. such as a keyboard, mouse,scanner, smart card etc.(b) Processing: A computer performs operations on the data and transforms it in some way.(c) Output: A computer gives an output on a device. such as a printer, a monitor or a plotter.(d) Storage: A computer stores the results of processing operations for future use, such as floppy disk. hard disk,optical disk, cartridge tape.Characteristics of computer:The important factors that lead a person to use a computer are:Speed.AccuracyStorage“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 2
  3. 3. Shree M. & N. Virani Science CollegeVersatilityDiligenceReliabilityMemory capability.Speed:Computers are very fast. They can process millions of instructions per second. Computers can perform inminutes, tasks that would take a person year to complete. Today, computers can perform 1000 millioncomputations in I second. The speed of computer is closely related to the amount of data it processes. Theterms used to describe the amount of data handled by a computer svstem are volume and frequency. Volumerepresents the overall quantity of data and frequency describes how often a specific data item is used inprocessing. Railway or Airline reservation system illustrates frequency.Accuracy:Computers are accurate. They do not make mistakes in calculations. The probability of computer error is quitesmall and often traceable to faulty data. Computer can perform allkinds of complex calculations -accurately. The degree of accuracy of computers depends upon their design.But, for a particular computer, each and every calculation is performed with the same accuracy. Errors incomputers are not of technological nature but are mostly due imprecise thinking of the programmer. The mainexamples in front of us are:(a) Space shuttles(b) Nuclear simulation reactions.Storage:Computers are having enormous storage capacity. Computers can store a vast amount of information, whichcan be recalled at any time in fraction of seconds. The information is stored in the form of files, but on disks andtapes. This helps in easy and speedy retrieval of information. This storage is known as electronic storagesystem. This system removes the duplication of information being stored. For example, in a company or anorganization the details of employees are given such as name. address. basic salary, unique code number etc.,that may be required by accounts department as well as personnel department. In case, an employee resigns oris promoted, then the updation of the information is required only once and at one place. Now a days standardstorage capacity of a computer is in the range of 20 GB- I 00 GB.Versatility:This is one of the most wonderful things about the computer. Computers can do a variety of jobs dependingupon the instructions fed to them and their hardware characteristics. Modern computers can be used inrailways. air reservations systems, process controls, nuclear reactors. manufacturing plants, scientificlaboratories, hospitals and hotels etc. They can also act as controlling devices in children toys. Briefly, acomputer is capable of performing any task provided that the task can be reduced to a series of logical steps.Their versatility can further be demonstrated by their use in cleaning the streets of a city, improving the existingsewage system to landing man on mars.Diligence:Computers are diligent in nature as they can perform complicated and respective tasks very well with fullconcentration. without committing any error, for long periods of time. Computers do not suffer fromcarelessness, boredom or tiredness. Moreover. their efficiency does not decrease with age. If millions of“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 3
  4. 4. Shree M. & N. Virani Science Collegecalculations are to be made with exactlv the same accuracy even then computer will not show any tiredness andcommit any error.Reliability:Computer systems are widely accepted due to their exceptional reliability. Unlike huma beings they are capableof operating under the most adverse conditions for extended period of time without showing any sign of fatigue.They do not take sick days and coffee breaks Computers are very reliable. We can consider them as veryfaithful super servants o humanity.Memory Capability:Computer systems have the capability to recall the total data instantly and an almost unlimited capacity to storethis data. A typical mainframe computer can have billions o characters and thousands of graphic images storedand available for instant recall.The above characteristics of computers enhance human capabilities of doing analytical work at high speed.It is important to mention that in spite of all wonderful characteristic of computers they had certain drawbacks.They have no I.Q. They have no feelings and cannot work like human beings.Advantages of Computer:Computers are having advantages over other computing devices as they are fast, reliable, accurate, can storemassive amounts of information, can move information quickly from one place to another and are versatile innature.The advantages of computers can be listed out as below-(a) Perform repetitive tasks.(b) Are more accurate while dealing with large numbers.(c) Work at constant efficiency.(d) Are used in almost every field.(e) Process millions of instructions in a fraction of a second.(f) Are effective and efficient data storage and retrieval.After having looked at the characteristics of a computer, the advantages of using it become very obvious. Theseare:(a) The speed at which the computer carries out its operations.(b) Its versatility, i.e. can be used in different fields.(c) Enable an individual or an organization to store and retrieve information as and when required.(d) Feeding of information is required only once in one Organization or company and the same can be used bydifferent departments of the Organization of company.(e) Instant recall of information is possible. Any format of reports can be taken about individuals, group ofindividuals etc.Limitations of computers:(a) Non-affordability: The high cost of installation of computers puts a limit over its use. However, due tothe advent of PCs and super mini-computers and mini super computers, a common man can also afford to buy acomputer.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 4
  5. 5. Shree M. & N. Virani Science College(b) Compatibility: Programs and software written for one type of computer or microprocessor cannot beused for other type of microprocessors.(c) Dependent upon human beings.(d) Have no imagination and intuition of their own.(e) Tasks have to be described in detail.(f) Cannot detect flaw or error in logic.(g) Need of an expert programmer: Today a large number of computer languages are in use and also there are lots of operating systems. Complete knowledge of system software (operating system) along with application software is a must. Computers process data in a step-by-step fashion according to the programs written for it. If any mistake occurs in programming, then an error is bound to occur in processing the data, which leads to wrong calculations in the output.(h) Unlike the human brain, a computer cannot think on its own, but has to be imparted instructions in a veryexplicit manner to perform a task. Even, instructions have to be given to prepare the reports as desired by theuser.(i) There is a lack of creativity and imagination. It does not have any advantage of its experience ofworking on the same program or different programs. Every task is new to it because it follows the instruction ofthe program.0) Non-standardization: A large number of versions are available and to use a given hardware andsoftware it is essential to have their complete knowledge of compatibility. No sincere efforts have been made sofar to standardize the various software and hardware.Applications of Computers:Today, computers have their utility in almost every sphere of life - particularly in the areas where calculations aredone at very fast speed. Computers now a day are being used in almost every department to do the work at agreater speed and accuracy. They can keep the record of all the employees and prepare their salary bill in amatter of minutes. They can also keep checks on the stock of a particular item. Big commercial houses andcompanies use software packages to control and monitor their production system, dispatch system. accountsystem and many more. These packages need high level of expertise to develop, use and maintain. Thesepackages cost huge amount of money.These days computers can be used for followings:(a) Materials Management(b) Production planning and control (c) Purchase(d) Credit and collection(e) Warehousing(f) Marketing information systems(g) Manufacturing information systems(h) Multimedia(i) Science and technologyj) Banks are using special software packages for monitoring their working. At any point of time theconcerned authority can have details of cash deposits, cheque deposits, overdrafts, interest charges on the loanamount etc., in a matter of minutes. -“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 5
  6. 6. Shree M. & N. Virani Science College(k) Schools are using special software packages for fee administration, finance, transport, time scheduling,and payroll Record of students, Performance of teachers.In future, computers will find extensive use in the areas ofInformation networksCommunicationsArtificial intelligenceParallel processingBiochipsVoice recognitionRobotsNegative effects of Computers(a) Computers may pose a threat to personal privacy, because every kind of data of a person can easily be Stored and recalled.(b) Computer manufacturing processes require the use of hazardous chemicals, which could endanger human lives.(c) Too much use of computer can result in painful nerve injuries, such as carpel tunnel syndrome.(d) In case of computer failures in a critical system, such as air traffic control system, lives may be endangered.(e) Computers may displace workers by automating tasks that people use to perform. Since computers work more efficiently and effectively therefore. fewer numbers of workers may be required in place of large Number. The displaced workers may lose their salary substantially ilat all they get ajob.Elements of ComputerIt is necessary to know the architecture i.e., the internal structure of a computer to understand the functioning ofa computer."A computer, as we have learnt, is an electronic device which accepts instructions and data, stores it as long asrequired, processes the given data according to the instructions (programs) given to it and gives the output asand when required".If we analyze the above information, we find computer system to essentially perform the following functions:(a) Accepts the information (Input).(b) Manipulates the information (Processing).(c) Stores the information (Storage).(d) Displays the result (Output).This definition is often referred to as IPOS cycle.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 6
  7. 7. Shree M. & N. Virani Science CollegeEquipment and program are two essential parts of a working computer system. In computer terminology, allcomputer programs are known as software and all computer peripherals are called hardware.HARDWAREThe term hardware refers to the physical parts of the computer. Computer hardware is versatile and it dependsupon the computer program you use.Hardware is a general term use to represent the physical and the tangible components of the computer itself i.e.,those components. which can be seen and touched. It includesInput devices.Output devices.Memory.Processor.Storage devices.The electronic circuits consisting of resistors, capacitors, ICs etc., inside a computer are all examples ofcomputer hardware. All input and output devices connected to the computer are collectively known asperipherals.Add-ons are boards containing chips and printed circuits which are inserted into slots on the main system boardfor the purpose of adding memory, graphics capabilities, co-processors, or other capabilities to the computer.The key to computers versatility is memory. We can think of memory as a temporary workspace. Thecomputers processor uses this workspace during processing. Memory is temporary and storage is usuallypermanent. On most computers, storage has far greater capacity than memory. To describe large capacities,the terms kilobyte (KB), megabyte (MB), and gigabyte (GB) are used. One byte equals only one character.Input Devices:These are the devices bv means of which data are entered into the computer system. The most common inputdevices are:(a) Kev board (Data entered of the keyboard is directly sent to the CPU. There is no intermediate step.)(b) Mouse (It is a pointing device. It is used to link keyboard to communicate with the computer.)(e) Readers of punched lards (These type of devices were very common in the, earlier years. Now keyboards are used.)(d) Paper and magnetic tapes (The data is first accepted from the keyboard and stored on magnetic tapes. From these tapes the datais sent to CPU.)(e) Light pen (This is used for drawing on the screen.)“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 7
  8. 8. Shree M. & N. Virani Science College(f) Joystick (This is normally used for playing computer games.)(g) Optical image scanners(It uses optical technology to capture the image from the image provided to it.)(h) MICR (Magnetic Ink Character Recognition) (It uses special ink to print characters which can be read and decoded by special magnetic devices. Thissystem is widely used by banks for processing cheques.)(i) OCR (Optical Character Recognition) (A scanner converts the image that it sees into numeric digits before storing the image in the computer.This conversion proves is known as digitising.)OMR (Optical Mark Reader)OMR uses optical technology to detect the presence or absence of mark in standard position on a form.)(k) Audio sensors. (Input in the form of sound waves sent to CPU)(m) Temperature sensors. (Temperature is measured and sent to CPU)Output Devices:These are the devices, which translate processed data from a machine-coded form to a form that can be readand used by people.When processing is complete in the CPU, the information produced is stored in the memory in a computerunderstandable format. This information has to be transcribed into a form that can be read by the user, which isachieved by output devices.There are two types of outputs produced by output devices:(i) Soft copy: An output on the VDU or stored on magnetic media such as magnetic disks and tapes.(ii) Hard copy: An output produced on a printer or a plotter,The most common type of output devices are:(a) Monitors (Monochrome or black and white, colour).(b) Printers“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 8
  9. 9. Shree M. & N. Virani Science College(Different types of printers are used with personal computers and they are classified by the method of printing.Mainly there are three types of printers connected to personal computers.Dot Matrix Printer, Ink Jet Printer, Laser Printer(c) Graphics plotters(a plotter is a device used for producing outputs such as blue prints etc. for example, flatbed plotters, drumplotters. Plotters come in different sizes such as A-4, A-2, A-1 etc.)A new type of output device used now-a-days is speech synthesizer; a software attached to the computer thatproduces verbal output sounding like human speech.Memory:Memory is electronic holding place for instructions and data that your computers microprocessor can reachquickly. When your computer system is in normal operation, its memory usually contains the main parts of theoperating and some or all of the application programs and related data in use.Memory is often used as a shorter synonym for random access memory (RAM). The primary memory section ofmemory is a part of CPU and usually consists of mixture of RAM and ROM. As secondary memory thecomputer may also have floppy disks, magnetic hard disk, or laser optical disks.Memory has two purposes.(a) To store the binary codes for the sequence of instructions to be carried out by the computer according tothe program written.(b) To store the binary-coded data with which the computer is going to be working. For example, inventoryrecord of a company or a market.Processor.It is also referred as the brain of the system. It is that part of the process the data which contains electroniccircuit to process the data. Depending on the instructions of input devices it performs operations on the data. Italso controls the flow of data through the system, directing the data to enter the system, placing it in memory andretrieving it when required and directing the output.The CPU consists of(a) ALU (Arithmetical Logic Unit): It takes logical decision and performs all type of arithmetical calculations.(b) Memory - It is the unit where all data, intermediate and final, are stored. The data from an input unit aretransmitted to computer memory unit where they are available for processing. This unit also holds theinstructions for processing of data.(c) Control unit - It controls all the activities of other units of computer system. It receives instructions frommemory unit. It decodes these instructions. It decides the routing and store of these instructions.Storage Devices:Many people confuse memory with storage. Memory is temporary. Everything in memory is lost when you turnoff the computer. Storage is usually permanent. Almost on all the computer systems, storage has far great orcapacity than memory.Most common storage devices are categorized as:(i) Primary storage devices.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 9
  10. 10. Shree M. & N. Virani Science College (a) RAM (Random Access Memory) (b) ROM (Read Only Memory)(ii) Secondary storage devices. (a) Floppy disk. (b) Hard disks. (c) Optical disks. (d) Cartridge tape. (e) Spool tape.SOFTWARE:The non-tangible components of computer system are, referred to as software.Software consists of the instructions to be passed to computer to perform the desired functions. Sequentialinstructions, which direct the system to perform a specific task is called a program. Making of these sequentialinstructions is termed -as programming. Programs may be simple or complicated based on number ofinstructions.Computer software can be broadly classified into three categories:(a) System software:Software, which has its orientation more towards the operation of the hardware components of the computersystem i.e., concerned primarily with coordinating and controlling hardware resources.Or,It is an integrated set of specialized programs that is used to manage the overall operations of a computer.The term system software is generally used to describe program that make computer more adaptable and easyto use. The system software makes available to the programmer all facilities that might be useful to developprograms.The examples of system software are:Operating systems.Assemblers, Compilers, Interpreters.Programming aids.Report generation.Telecommunication programs.Utility or service programs.Editors.For example, DOS, Windows498, Windows-NT, Unix, Linux etc.(b) Utility software:The software, which has its orientation more towards facilitating the use of computer and the various applicationsoftware, is called utility software.For example, calendar, calculator, software to manage data stored on the disk, etc.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 10
  11. 11. Shree M. & N. Virani Science CollegeThese are the programs used to perform specific talks like duplication,copying etc.(e) Application software:The application software are created for specific use. They are not common usage programs. These are theprograms, which direct the computer to perform a specific task as desired by a user, such as printing of mailinglist, printing of payroll of employees. These programs are available in the. Areas of business, education,manufacturing applications, desktop publishing, designing, graphics and web browsing.They provide flexibility. We can modify and change the programs . when requirements change. Normallysource codes for application programs are available for modification.Application programs are written in higher level programming languages such as COBOL, C++, VISUAL BASIC,JAVA etc.INPUT/OUTPUT DEVICESComputers are known for their speed and accuracy. But to do some work i.e., to process it requires some data.Raw data is to be given to the computer which is expected to be converted into information after process- Inshort, the working of the computer can be understood as any machine, which requires some input, processes itand produces the output. Graphically it may be understood as:Input DevicesTo process, the computers need raw data. This raw data is to be input to the computers using certtain devicesknown as input devices. Today, a large number of input devices are available in the market suiting our variousrequirements.Input devices transfer data into a computerized information system so that it can be reused. Remember, that thecomputer does not process information it processes data.Here are two different categories of input devices:(a) Manual Input Devices:With a manual input device the user must enter data into the computer by hand e.g. mouse, keyboard, scanneretc.(b) Direct Data Entry Devices:Direct data entry device can transfer information automatically from a source document ---- as form or barcodeinto the computer. The user does not need to manually enter the information e.g., optical mark recognition etc.This device resembles a typewriter and is today the most widely used device to input information in the form ofwords and numbers. This layout of keys is called QNWRTY because Q-W-E-R-T-Y is the order in which theletters occur on the top row of the keyboard. Like typewriter keyboard contains alphabetic, numeric and specialcharacters. Unlike typewriter, which records the data on the paper, each character keyed in, using keyboard isencoded into the computer systems data coding scheme and is stored in computers memory.Along with normal expected keys the special keys include, Control, Shift, Alt, Return, Escape, Arrow keys andFunction keys (Fl to F10 or F12).Applications make use of the keys according to their requirement.For example,“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 11
  12. 12. Shree M. & N. Virani Science College F2 is used by many applications to save data permanently. Fl is frequently used to provide context sensitive help to the users. Page Up, Page Down, Home and End keys are used for cursor movements. Caps Lock is used to type in capital letters. Num Lock is used to toggle the use of numeric keypad available on the keyboard. Shift keys can also be used to type in uppercase or lowercase according to the on or off of the Caps Lock key. Pointing Devices When the interface is graphical one easier way of selection and feeding information to system is the pointing device. Various pointing devices available are: The mouse and Track ball Mouse comes in sizes slightly bigger than Indian Match box. It rolls over bearing. When the user rolls the mouse across a flat surface, such as desk, the screen cursor moves in the direction of the mouses movement. It becomes very easy in the graphical environment like that of Windows to move, cut, copy, paste or open files and folders using this pointing device. Tracker ball is something similar to the mouse but less complicated and designed for use by ".children. This has got a spherical ball, which can be rotated by fingers in various directions to affect screen movements. Touch Pad· is a small device, which can be embedded directly into various systems like laptops and -,books. Pointing devices like mouse does not find place with such devices because they mainly used for mobile computing. A separate device for input does not match the idea for compact and lesser space. The user can move his finger on the touch pad surface and .Luc input just like the mouse. Joystick Joystick resembles a stick and is used as input device, specially, in game and multimedia software. The type of input from this device mainly comprises of the movement of cursor on the screen or movement of screen output in various game software. The best joysticks, called analogue joysticks measure how far the joystick is being moved in the direction it is being pulled. This information is used to set how quickly the object on the screen moves. The further you push the joystick the faster the object moves. Small joysticks, called track-point devices, are sometimes built into the keyboards of portable computers and used instead of mouse. Touch sensitive screens Small touch sensitive boxes are provided on the screen of the monitor itself, which act something like the function keys present on the keyboard. The idea is to dispense with the keyboard and allow data to be input by touching the screen with the fingertip or other unit provided for the same purpose. This form of input is particularly suitable to applications design for use by the general public, for example, searching library catalogue files. Though it is very user friendly but a large amount of data cannot be input using this device and only the “Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 12
  13. 13. Shree M. & N. Virani Science Collegefunctions like selection and pointing can be done. Touch screens are not used very often, as they are not veryaccurate, tiring to use for a long period and are more expensive alternatives like a mouse.Pen based systems. Light pen is another pointing device similar to any normal pen and can be used effectively to input data.Proper software can be used to input data in users own handwriting and can be also useful for graphical work,for example, the user at a computer aided design (CAD) terminal can draw directly on the screen with the pen.Data scanning devicesThere may be need that the input is not to be given in words or numbers but through are available data typed ona page. Various available data scanning devices can be used to scan and input data through availabledocuments. Various available data scanning devices include:Optical recognition systems(a) Barcode reader (BCR) scans a set of vertical bars of different widths for specific data and are used to read tags and merchandise in stores, medical records, library books etc. It is a direct data entry device.Barcodes are often printed on products that we buy and are used to produce bills for customers. The number isoften printed above or below the bar code so that humans can read it.Barcodes are read into computer using a moving or a fixed scanner. Barcodes are not easily damaged and cannormally still be read if they are creased or not stuck onto a flat surface. They can be printed using a normalprinter and ink and so are cheap to produce. The information normally included on bar code for a product iscountry of origin, manufacturer and item code. The price is not included in the bar code.(b) Optical mark reader (OMR) this device is used mainly to recognize marks made by pencil or pen. The device can be used in various competitive exams where the method of examination is objective type and the candidates are required to fill the answer sheets with pencils. For such type of exams pre-printed answer sheets with containing boxes or squares for correct answers are used. The candidates are required to fill the desired box or square with lead pencil.The reader detects where the marks are placed by shining a light at the page and measuring the amount of lightreflected. Less light is reflected where the marks have been made.Input using OMR is accurate and very fast. Problems can occur if the OMR forms get creased as the-readermay jam.(c) Optical scanners can be used to scan images, posters, magazine pages, other physical objects like ornaments etc., and can be directly stored into computers memory. This device is particularly useful for multimedia producers who need to input large amounts of printed historical text and turn it into searchable data.The optical sensor reads information about one line of the image at a time. They must be moved down thepicture to input the whole image. There are two different types of scanner: (i) Flatbed Scanner: You place the image on top of the scanner. The scanner moves the light andsensor itself and scans the whole image automatically. Most flatbed scanners are A4 size. (ii)Handheld Scanner: You must manually push the light/sensor along the image. Handheld scannersare usually 5 inches wide.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 13
  14. 14. Shree M. & N. Virani Science CollegeFlatbed scanners are better as they can scan larger images and are more accurate than handheld scanners. Onthe other hand, handheld scanners are cheaper and more portable. The price of flatbed scanners has fallen somuch in- recent years that handheld scanners are rarely sold now.Some other known input devices are as follows:(d) Magnetic Ink Character Recognition (MICR)The MICR system reads characters printed in special magnetic ink into the computer. The main users of MICRare banks. They use it to read information from cheques into their computers so that the cheques can becashed. Here is some information stored on a cheque using MICRThe information printed on the cheque using MICR is • A unique number for the cheque. • A code that identifies the bank and branch that issued the cheque. • The number of the account that the cheque relates to.MICR readers can only read one special font, which can represent only numbers and a few punctuation marks.They can read characters very quickly and with 100% accuracy. Information printed in magnetic ink is also verysecure. It is not possible to change the (information by writing over it with a pen, and the printed numbers arenot damaged by folding (as often happens with cheques). Both the reader used by NUCR and the special inkare expensive.(e) Optical Character Recognition (OCR)An optical character recognition system consists of a scanner and some software. The scanner is used to scanan image of a page of text to be read into the computer. The software examines the page and extracts the textfrom it, storing it in a form that can be processed.OCR systems can now recognize a wide variety of computer fonts and read letters with o 95% accuracy. Somesystems will recognize hand-written text reasonably well as long as it is written very neatly and usually put intoboxes on a pre-printed form.Voice recognition systemsThese devices can directly take input in the form of human voice and translate it in digital, form understandableby the computers. The device finds its usage in modem offices where managers need to dictate letters andother official documents and want to save time and stationary in first dictating the matter to write and then toconvert it to digital form through keyboard.Voice recognition systems listen to what people are saying and carry out the instructions given to them whenpeople speak. A microphone is used to provide input for a voice recognition system. Currently, these systemsare not very sophisticated and are used only for certain applications. Existing voice recognition systems come intwo different types:(a) Systems, which recognl2;e only a few words but can understand most peoples voices e.g. telephone banking computers.(b) Systems, which recognize a wide vocabulary but need to be trained to understand each different voice e.g. automatic dictation systems.In the last few years a number of voice dictation packages have been developed. packages let the user dictatetext into a computer to appear in a word processor d Dictating like this can be much quicker than typing but thecomputer still mat mistakes especially with short words.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 14
  15. 15. Shree M. & N. Virani Science CollegeOutput devices.The input data are to be processed and need to give certain output. The devices used to the output from thecomputer are known as output devices. An output device takes data from the computer and converts this intoinformation in a form, which is normally understandable by humans. Various output devices available are:MonitorsIt is also known as video display units (VDU) or simply screen. This is the most widely used capacities and isavailable in medium to view the output. it comes in various sizes and various modes for text and graphicaloutputsAn image displayed on the screen is made up of lots of dots called pixels. If you look at the screen you may beable to see these pixels. The resolution of the screen is "how many pixels there are up and down and from leftto right across the screen".A variety of resolutions are available. For PC these resolutions have names e.g. VGA is 640 x 480. This meansthere are 640 pixels in each row across the screen and 480 pixels in each column up and down the screen.SVGA is usually 800 X.600. Displays with lots of pixels are called high resolution. Displays fewer pixels arecalled low resolution. High-resolution display can show much more detail than low resolution ones and arerequired for applications, such as Computer Aided Designing and Multimedia.Cathode ray tube (CRT)It resembles television and takes input from the CPU and displays data. It has separate storage of about I kg,.capacity in the form of core or I.C. memory. The memory relieves the computer during display by storing thedata. The more sharper the image can be displayed, the unit is said to be having more resolution.Flat panel monitorsThese form the latest in display technology. it takes less power to move molecules than to energize a light-emitting device like CRT. Flat screen monitors first used only in notebook computers a re fast invading thedesktop. The completely flat screens sharply reduce reflection from the users environment and eliminate glare.Liquid Crystal Display:Besides the displays discussed above, the latest in the field is the Liquid Crystal Display. These displays arecompletely flat and so can be used in portable computers and other small devices such as calculators. They aremore expensive to make than desktop monitors. Currently, only the most expensive ones are as high quality asdesktop monitors. In ten years time LCDs will probably replace bulky desktop monitors.Audio outputThis unit permits the computer to talk back to us. This makes computer an excellent interactive medium to workwith. All the sounds needed to process the possible enquiries are pre-recorded on a storage media. Eachsound is given a. code when enquiries are received. The processor follows a set of rules to create a replymessage in coded form. This coded message is then transmitted to an audio response device, whichassembles the sound in the proper sequence and transmits the audio message back to the station requestingthe information.On PCs you also need to install a Sound Card to be able to output sound. If you want you @can connect thecomputer to a hi-fi to et louder, better quality sound than you would if you, plugged the loudspeakers straight intothe computer. The sound produced by PC-s is now of better quality than sound that is recorded on a CD.With proper software a computer can read out text that has been printed into it by using a computerized orrecorded voice. This type, of system is known as speech synthesis.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 15
  16. 16. Shree M. & N. Virani Science CollegePrinters.The hardcopy of the data stored in the computers memory is taken through printers, which is also an outputdevice like VDU. Printers can also be classified according to their nature. These are needed to produce a hardcopy output. Unlike images on a screen hard copy can provide a permanent record of work and can be lookedat away ftom the computer. Hard copy can be obtained using a printer or a plotter. There are lots of differenttypes of printers and plotters available. They vary in the method they use to produce hard copy and the cost andthe quality of the hard copy they produce. Different devices are suitable, for different applications. Following isthe tree of printer family according to their classification: Hard copy output device Printer Plotter Impact Non-Impact Flatbed Drum Dot Matrix Daisy Wheel Line Laser Ink Jet ThermalPrinters can be divided into following categories:Impact printersThe technology uses the direct mechanical contact between the print head and the paper. These use variationsof standard typewriter printing mechanism where hammer strikes paper through inked ribbon. Because of thehammering action impact printers are noisy when they are printing. Various types include solid font and dotmatrix printer.Daisy Wheel PrinterDaisy wheel printers are rarely used any more. A daisy wheel printer hammers character stamps (like those ontypewriters) against a ribbon to produce high quality text output. The character patterns are all arranged aroundthe edge of a wheel. When a letter is to be printed the wheel rotates so that the correct letter is against theribbon to print it on the paper. Daisy wheel printers are very slow and noisy. It is not possible to print graphicsusing a daisy wheel printer.Line PrintersDot matrix and daisy wheel printers both print only one character at a time. For that reason they are calledCharacter Printers. In contrast a line printer prints a whole line (typically 80 or 132 characters) of text at a time.These printers are very fast. They are expensive to buy and are used when high volumes of output are required.Example applications include printing telephone bills or bank statements.Non-impact printers:These printers use technology where there is no direct contact between the print and paper giving longer life tothe print head. They print characters by spraying small drops of ink on to paper. Because there is no hammeringaction non-impact printers are very quite but cannot print multiple copies using carbon paper. Examples includeinkjet, laser printer etc.Laser Printer“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 16
  17. 17. Shree M. & N. Virani Science CollegeLaser Printers are called Page Printers because they print a whole page at a time. A laser beam is used to drawthe image to be printed onto a light sensitive Drum. After the image has been drawn on the drum, fine powderink called Toner is put onto it. The toner only sticks where the laser has drawn the image. The paper thenpasses over the drum and the toner is transferred onto the paper.Laser printers produce very high quality output, are very quiet and very fast. Typical home laser printers canprint 8 pages per minute (ppm). Some industrial versions print over 40ppm and can print on both sides of apiece of paper at the same time.-,,The main disadvantage of this type of printer is the high cost.Inkjet PrintersInk jet printers are the most popular t .Ype of printer for use at home or in a sma I business. This is becausethey are relatively cheap to purchase and can print in colour. Ink jet printers generate output by squirting tinyjets of ink at the paper to be printed on. A column of ink jets in the print head moves across the page squirtingdots onto the page to make the image. Typically ink jet printers can produce 360 or 720 dots per inch (dpi) butthese dots are larger than those that a laser printer makes so the quality, although very good, is not quite asperfect. Ink-jet printers can work in black and white or colour.STORAGE DEVICESStorage devices are used to store every kind of data. The concept of data covers important business facts andfigures and various other official documents. Data is a backbone of any business and proper storage andretrieval of data is a must.Computers are known for their speed and accurate calculation capabilities but if the data is not saved properly,then everything will be in vain. Thus, storage of data is an important concept and various technologies areinvolved in this concept. Here -we will try to understand various technologies and devices capable of storing andretrieving data.The main points those should be kept in mind in terms of storing data are:(i) Storage should be economical,(ii) It should be secure and safe(iii) Data storage device should be capable of storing almost unlimited amount of data.Storage in computers is classified as two typesa. Internal1. RAM2. ROMb. ExternalWhere Internal storage is the computers own storage, which is further classified into two types RAM and ROM.On the other hand external storage is nothing but the external devices that has to be attached with computer inorder to have the data stored in it. External storage devices can be named as Floppy Disks and Compact Disketc.Let us take the example of a Audio cassette player that plays a music cassette in it. When we play a audiocassette in the Audio Cassette Player it is played and we are able to hear music on the speakers, but the“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 17
  18. 18. Shree M. & N. Virani Science Collegemoment we take out the cassette the music is no more played. But on the other hand a computer will keep onrunning the software on the screen even if the floppy disk is removed from the drive and kept outside. This isbecause of the fact that the computer initially reads the information from a floppy disk and store it in RAM once itis fully stored in RAM even if the disk is removed from the drive the software keeps on running. Hence RAM isthe most essential part of the computer. In simple language we can say that whatever we are viewing on thescreen is present in the RAM. RAM stands for Random Access Memory, which is temporary memory in itself. Ifthe computer is switched -off while on it, whatever is there in the RAM goes off and next time we have to reloadthe entire thing. This is the reason we have to save the file we are working on.On the other hand ROM stands for Read Only Memory, which is a permanent memory in it ROM is basicallystoring the computer startup instructions in it. Whenever we switch on our computer it performs a self-checkbecause of ROM. Instruction in ROM are permanent i.e. once fed by the manufacturer of the computer and cannever be changed by the user. Software permanently embedded in Hardware is called as FIRM WARE.Storage devices discussed here are also known as secondary, auxiliary or back up storage. Secondary storagedevices can be used to store programs and data in a machine-readable form for processing at a later date, or forholding data on a temporary basis during the processing of a program. It provides a means of retaininginformation on a permanent basis.Besides providing space for retaining working file, secondary device may be used to retain copies of files. Thesecondary storage is external to the CPU. A secondary device is therefore also a peripheral device, just as anyinput or output device.Various types of devices are available for data storage. These include:Magnetic Storage Devices.These devices use electromagnetic principles to store data. The devices normally take shape of circular disks.Data are recorded on disk in concentric circular bands called tracks. The tracks on a disk are similar to thegrooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors. Two or moresectors combine to form cluster.Magnetic devices like -floppy disks, hard disks and some tape units all use the same underlying technology toachieve this. The media (meaning the disk as opposed to the drive) is coated with magnetic particles a fewmillionths of an inch thick, which the drive divides into microscopic areas called domains. Each domain acts likea tiny magnet, with north and south poles, and represents either zero or one depending on which way it ispointing.Available devices of such type are:Diskette drives:Also known as floppy disks, it is a flexible circle of mylar plastic. It comes in two sizes viz. 5.25 inches and 3.5inches in diameter respectively. 3.5 inches floppy are newer and capable of storing more data because of newertechnology used in such device, making 5.25 inches floppy drives nearly obsolete.The density of magnetic particles on the disks surface determines the amount of data that can be stored on afloppy disk.The head is moved by a lead-screw, which in turn is driven by a stepper motor; when tie motor and screw rotatethrough a set angle, the head moves a fixed distance. The data density of floppies is therefore governed by theaccuracy of the stepper motor, which means 135 tracks per inch (tpi) for 1.44MB disks. A drive has foursensors: disk motor; write-protect; disk present; and a track 00 sensor, which is basically an edge stop.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 18
  19. 19. Shree M. & N. Virani Science CollegeThe magnetic head has a ferrite core, with the read/write head in the centre and an erase head core on eitherside. The erase heads wipe out a strip either side of a new data track to avoid interference from old data tracks.Bits are stored as magnetic inversions, the inversion intervals being two to four microseconds (µs). The readsignal goes to a peak detector and is processed to produce a binary signal by the electronics in the drive. This isthen sent back to the PC.Floppy disks head actually touches the diskette as a result both the media and the heads wear out early. Tracklife for a diskette is generally on the order of 3 to 5 million contact revolutions.Floppy comes in low density and high-density versions each affecting the amount of data that can be packed inthe single unit of the diskette.Future of floppy disks:The 200MB to 300MB range is best understood as super-floppy territory. This is about double the capacity ofthe would-be floppy replacements with performance more. similar to a hard disk dm a floppy disk drive. Drivesin this group use either magnetic storage or magneto-optical technology. The magnetic media drives offer betterperformance, but even MO (Magneto-optical drives, discussed later) drive performance, at least for the SCSIversions, is good enough to allow video clips to be played directly from the drives.Hard Disks:It is made of rigid metallic platters and functionally works same as floppy disks. These are generallypermanently encased in the disk drive. These are capable of storing large amounts of data in range from 10 MBto more than 20 GB (gigabytes). These disks drives can have four or more disk platters in sealed unit. In mostof these disk units the read/write head never touches the surfaces of the disks thus, giving more life to the diskas compared to floppy disk where there is a mechanical touch between the disk and the read/write head.Because of capable of storing huge amount of data and capability to read and write data at more speed theseare used widely in microcomputers.When a disk undergoes a low-level format, it is divided it into tracks and sectors. The tracks are concentriccircles around the central spindle on either side of each platter. Tracks physically above each other on theplatters are grouped together into cylinders, which are then further subdivided into sectors of 512 bytes perpiece. The concept of cylinders is important, since cross-platter information in the same cylinder can beaccessed without having to move the heads. The sector is a disks smallest accessible unit.Drives use a technique called zoned-bit recording in which tracks on the outside of the disk contain more sectorsthan those on the inside.Theres a read/write head for each side of each platter, mounted on arms, which can move them towards thecentral spindle or towards the edge. The arms are moved by the head actuator, which contains a voice-coil - anelectromagnetic coil that can move a magnet very rapidly. Loudspeaker cones are vibrated using a similarmechanism.There are typically 3000 tracks on a platter side. Data is stored on both sides of the platter. Separate arms areprovided with read/write heads to read and store on these platters. The read/write head consists of tinyelectromagnetic. The shape of the head end acts like an airfoil, lifting the read/write head slightly above thespinning disk below.When the disk rotates under the read/write head. it can either read existing data or write new ones. If a currentis applied to the coil, the head will become magnetic. This magnetism will orient the micro magnets in the track.This is write mode.When the head moves along the track without current applied to the coil, it will sense the micro magnets in thetrack. This magnetism will induce a current in the coil. These flashes of current represent the data on the disk.This is read mode.Removable hard disks:“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 19
  20. 20. Shree M. & N. Virani Science CollegeHard disk are encased in the disk drive. This makes the data transfer an issue of concern from one place toanother. The capacity of floppy disks is much less, so more data cant be transferred at a time. This generatesthe need of removable hard disk that can store large amount of data as well the unit can be detached from thecomputer system easily and could be relocated to another system easily.Optical Storage devices:These form the second category of storage devices. These are most advanced in terms of technology used.These devices use optical (LASER) technology to access data. This makes the life of device high and morereliable for data storage. The technology involves a high power laser beam to bum microscopic spots in diskssurface coating.Available devices using this technology are:Compact Disk Read Only Memory (CD ROM)The CDROM is a thin piece of clear polycarbonate plastic with a metal layer covered with a protective layer oflacquer, with the aluminum layer measuring 120 mm in diameter. It is mostly useful in multimedia applicationswhere data is huge and needed to be transferred from one place to another and the requirement is of securedata. The disk can also be used to distribute songs that also require huge amount of space and to distributebundled software packages. The main disadvantage of this type of media is that they are read-only that meansdisk manufacture can only data on them and rest can only read from it. But this point is also a strong point infavor of using them because this makes them safe against any kind of accidental or purposeful destruction ofdata.CDs measure 12cm in diameter with a 15mm diameter centre hole. The audio or computer data is stored fromradius 25mm (after the lead-in) to radius 58mm maximum where the lead-out starts. The Orange Book CD-Rstandard basically splits the CD into two areas: the System Use Area (SUA) and the Information Area. While thelatter is a general storage space, the SUA acts much like the boot sector of a hard disk, taking up the first 4mm.of the CDs surface. It tells the reader device what kind of information to expect and what format the data will bein, and is itself divided into two parts: the Power Calibration Area (PCA) and the Program Memory Area (PMA).CD-Recordable (CD-R), WORM and Photo CDThe disadvantage of CD ROM is removed by using what is known as WORM disk (Write Once Read Many).This allows to write on disk at users choice but once written the data cannot be altered later.The characteristics of a CD-R were specified in the 0 range Book 11 standard in 1990 and Philips was first tomarket with a CD-R product in mid-1993. It uses the same technology as WORM, changing the reflectivity of theorganic dye layer, which replaces the sheet of reflective aluminum in a normal CD disc. In its early days,cyanine dye and its metal-stabilized derivatives were the de facto standard for CD-R media. Indeed, the OrangeBook, Part 11, referred to the recording characteristics of cyanine-based dyes in establishing CD-Recordablestandards.Phthalocyanine dye is a newer dye that appears to be less sensitive to degradation from ordinary light such asultraviolet (UV), fluorescence and sunshine.Also dye has been used in other optical recording media and is now also being used in CD-R.These dyes are photosensitive organic compounds, similar to those used in making -photographs. The mediamanufacturers use these different dyes in combination with dye L,4uckness, reflectivity thickness and materialand groove structure to fine tune their recording characteristics for a wide range of recording speeds, recordingpower and media longevity. To recreate some of the properties of the aluminum used in standard CDs and to“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 20
  21. 21. Shree M. & N. Virani Science Collegeprotect the -d ye, a microscopic reflective layer-either a proprietary silvery alloy or 24-carat gold - is coated overthe dye.el use of noble metal reflectors eliminates the risk of corrosion and oxidation. The CD-R media manufacturershave performed extensive media longevity studies using industry .Red tests and mathematical modelingtechniques, with results claiming longevity from 70 op to over 200 years. Typically, however, they will claim anestimated shelf life of between 5 and 10 years.OPERATING SYSTEMSThe present day computer is perceived as a very fast and accurate electronic machine that is designed toautomatically accept, store input data, process it and produce output results under the directions of a storedprogram of instructions.The physical and tangible components of this machine are termed hardware and the sets of instructions storedas programs that govem its operations and turn the h/w merchandise into a usable system is termed assoftware.Furthermore, the s/w part that contributes to control and performance of this system are categorized as systems/w, mainly meant to recognize, synchronize and process inter-hardware communication.The specific task or purpose oriented user programs like accounting, designing are categorized as applicationsoftware.The physical resources of such a machine are the processor, main memory storage devices and 1/0 devices.The fundamental part of system software, which primarily-controls, manages and provides a centralized accessto the machine resources, is the operating system. The operating system provides an interface or a virtualmachine. which keeps away user from the complex internal h/w functioning and acts as a basic platform for theapplication programs to run.Hence the information sciences see the functionality of the operating systems as1. An extended or virtual machine provider2. A resource managerExamples of various modem operating systems are DOS, WINDOWS 95, WINDOWS98, UNIX, LINUX etc.COMPUTER SYSTEM STRUCTUREThe computer system structure is based upon the various levels of functionality and interaction between a userand the system machine intervals. The execution of the machine is alienated from the user by some bottomlayers. Levels of transparency between layers increase as we move from bottom to top layers. Based upon this,the structure is divided into 6 layers with categorization into 3 basic levels:6. HIGH LEVEL LANGUAGES, WORD PROCESSORS [APPLICATION PROGRAMS]-------------------------------------------------------------------------------------------5. COMPILERS, EDITORS, INTERPRETERS [SYSTEM PROGRAMS]---------------------------------------------------------------------------------------------“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 21
  22. 22. Shree M. & N. Virani Science College4. OPERATING SYSTEM [SYSTEM PROGRAMS]---------------------------------------------------------------------------------------------3. MACHINE LANGUAGE [H/W]----------------------------------------------------------------------------------------------2. MICROPROGRAMS [H/W]---------------------------------------------------------------------------------------------1. PHYSICAL DEVICES [H/W]--------------------------------------------------------------------------------------------When a user works on a computer on any application e.g. DocumentProgramming language like C++, he writescommands in English language in proper format and syntax. They are first checked and interpreted byapplication programs specifically meant for the purpose e.g. compiler like a turbo C++ compiler. Thisinterpretation works using operating system like Win98/NT as a basic platform which further makes thistranslated set of instructions available to the Machine and Machine in turn translates it into its own languagecalled Machine Language or the Binary Language. The final process involves making the tangible H/Wunderstand the language by the instructions implemented in the physical device itself by the manufacturer andthis instructions se t is called a micro-program e.g. system BIOS. The physical devices like HARD diskdrives/CD-ROMs respond as per the binary instructions.The bottom 3 layers of the Devices, Micro-programs and Machine language are completely alienated from theuser so it is taken as part of H/W. The O/S and the compilers etc. provide management and control functionswith apparent levels of transparency between user and this virtual machine and are termed system programs.The topmost layer, which directly interacts with the user, are termed application programs.OPERATING SYSTEM CONCEPTSA user of a computer system interacts directly with an application software program for his purposeful task. Thetask works over a platform which is the O/S.History & Evolution of Operating SystemsThe history & evolution of operating systems can be viewed in relation to the history & evolution of computersystems over the time. The computer system evolution has been broadly classified into four generations, whichalso led to the development of operating systems as per need and demand of users.1. ZEROETH GENERATION: MECHANICAL PARTS:Charles Babbage, an English mathematician, designed the first digital computer using wheels, gear etc. But themachine so developed was slow and unreliable.2. FIRST GENERATION (1945-1955): VACUUM TUBES:The mechanical design of earlier generation changed to electronic design using the vacuum tubes. Themachines thus formed were huge and generated lot of heat during running. Till this time switches were used to“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 22
  23. 23. Shree M. & N. Virani Science Collegefeed a calculation for each word, the counter was set to the first word and a start button was pressed to get theoutput in the form of lights and bulbs.3. SECOND GENERATION (1955-1965): TRANSISTORS:Around 1955 Transistors were introduced in the USA at AT&T. The machines using these transistors usedswitches for feeding input and light and bulbs for output as before.The entire operation of pressing several switches for each word was very time consuming.The solutions developed for faster processing comprised of the following:Step1Reduce the loading time and human involvement-prepare an offline job card and feed it to the result.For each calculation to be performed a different job card was needed to be prepared and loaded which wasagain very time consuming because of repetitive switching On/Off of the computer system. The solutionproposed was that on start up itself a computer should read a loader program, which further loads anothercomplex program. The complex program was specially meant to process the job cards. Then assemblylanguage emerged and programmers jobs was simplified The job cards (batch processing systems) now weresubstituted by assembly language programs. This entire process of switching on the machine and successiveloading of programs was called booting.Step2Improve the output and get textual results.The monitors evolved to act as principal output device. Apart form the monitors the printers were alsodeveloped.Step3Improve the input and feed textual entries.The keyboards were developed which acted as principal input and the interface device the user and thecomputer.With the development of transistor technology faster processors were produced which could produce resultsvery quickly. The system processor however, remained idle for most of the time during input feeds.Step4Faster speed to cope up with faster processor.Other hardware had to be modified for equivalent faster speeds giving rise to faster keyboards, 1/0 devices etc.Faster disk drives were also developed.In 1960 the first operating system oriented computer ATLAS was developed at Manchester University.4. THIRD GENERATION (1965-1980): INTEGRATED CIRCUITSIBM announced system/360 series of computers in 1964. The interrupts were developed. Single stream batchprocessing changed to Batch multi-programming.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 23
  24. 24. Shree M. & N. Virani Science CollegeA series of jobs were loaded in one go, which were processed one by one by the processor. If the processorneeded to wait for input- output device response for a job it could in the meanwhile process another job. Thusthe concepts of foreground and background processes were developed.IBM also provided utilities such as Simulators and Emulators to enable old software to be run on IBM 360 familyof computers. But it was found that operating system of large machine created problems When run on smallmachines and also the operating system of small machine were ineffective on large machine So IBM deliveredfour operating systems within same range of computers. These wereDOS/360 for the small 360 systemsOS/MFT for the medium 360 systemsOS/MVT for the bigger 360 systemsCP-67/CMS for the powerful 360/67, using virtual storageThus the concepts of family of computers and operating systems evolved.The concept of spooling was developed during this period.The concept of time-sharing and multi-programming (execution of many simultaneous programs) was enhancedgiving rise to another popular operating system called MULTICS (Multiplexed Information and ComputingService). It was a joint effort of MIT, Bell Labs and General Electric. It served to create a computer utility whichcould support hundreds of simultaneous time sharing users. Later on the name UNIX was adopted which ispopular till date.The only problem with this system was that it was not portable for different architectures because it was writtenin assembly language. Then a computer scientist Dennis Ritchie designed and implemented a high levellanguage called C and rewrote whole of UNIX in C language. The new system made an application written onUNIX 90% portable after which the UNIX source code was made available to many Universities freely. Latermulti user versions of LNIX were developed.5. FOURTH GENERATION (1980-1990): LARGE SCALE INTEGRATION:With this technology thousands of transistors could be packaged on to a single chip. This helped in producingdifferent computer modules like Resistors, Adders, Multiplexers, Decoders and a variety of other digital circuits.A new design of computers called as microcomputer evolved which was developed on Intel 8080 in 1974. Thisdesign became popular because of its user friendliness.After the advent of the IBM-PC based on Intel 8086 and then its subsequent models, the Disk OperatingSystem (DOS) was written. Finally a company called Microsoft Corporation acquired the rights for QDOS( Alater version of DOS) and produced its operating system as MS-DOS. Later on with the development of 386,486 and finally Pentium Processors, new operating systems based on Graphical User Interfaces (GUIs) havebeen developed e.g. windows 3.11, Win95, Win98, WinNT etc. which are popular till date. WinNT/NovellNetware like operating system are products meant for another type of computing called distributed processingand serve as true Network Operating System. Newer operating systems are currently under development, whichwill enhance multi-programming and powerful computing making the latest era of real-time computing and onlinecomputing truly possible with the aid of marvel tool INTERNET.Kinds of Operating SystemsBatch Processing SystemsIn earlier computers, the users didnt interact directly with the system, instead, a user prepared a job, whichconsisted of program, data, and some control information about the nature of the job and submitted it to the“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 24
  25. 25. Shree M. & N. Virani Science Collegecomputer operator. The operating system of such computer had the function to transfer the control from one jobto another. To speed up processing, jobs with similar needs were batched together and were run through thecomputer a group. Thus, the programmers would leave their programs with the operator. The operator wouldsort programs into batches with similar requirements and, as and when the computer became available, wouldrun each batch. The output from each job would be sent back to the appropriate programmer.A batch operating system, thus, normally reads a stream of separate jobs, each with its own control cards thatpredefine what the job does. When the job is complete, its output is usually printed. The definitive feature of abatch system is the lack of interaction between the user the job while job is being executed. The job is preparedand submitted and at some later time the output appears. The delay between job submission and jobcompletion may result from the amount of computing needed or from delays before the operating system startsto process the job. OPERATING SYSTEM USER PROGRAM AREA Memory layout for a simple batch system.In this execution environment, the CPU is often idle. This idleness occurs because the speeds of themechanical I/O devices are intrinsically slower than those of electronic devices. Even a slow CPU works in themicrosecond range, with thousands of instructions executed per second. A fast card reader, on the other hand,might read 1200 cards per minute. Thus, the difference in speed between the CPU and its I/0 devices may bethree orders of magnitude or more. Unfortunately, CPU speeds increased even faster, so that the problem wasnot only unresolved, but also exacerbated.Multitasking Systemsa. Multitasking (or TIME SHARING) is a logical extension of multiprogramming.b. In Multitasking Multiple jobs are executed by the CPU switching between them. It is of two types -> Pre-emptive multitasking -> Co-operative multitaskingPRE-EMPTIVE MULTITASKING/NON PRE-EMPTIVE (CO-OPERATIVE)CPU scheduling decisions may take place under the following 4 circumstances:1. When a process switches from the running state to the waiting state, (for e.g. I/0 request or invocation of waitfor the termination of one of the child processes)2. When a process switches from the running state to ready state (for e.g. when an interrupt occurs)3. When a process switches from waiting state to the ready state (for e.g. completion of I/0)4. When a process terminates.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 25
  26. 26. Shree M. & N. Virani Science CollegeWhen scheduling takes place only under circumstances 1 & 4, we say the scheduling scheme is non-preemptive(co-operative) otherwise the scheduling scheme is preemptive.Windows 3.11 operating system uses co-operative multi-tasking.Windows 95 and later operating systems use preemptive multitasking.TIME SHARING SYSTEMSTime-sharing is a logical extension of multiprogramming. Multiple jobs are executed by the CPU switchingbetween them but the switching occur so frequently that the uses may interact with each program while it isrunning.Time sharing systems were designed to produce interactive use of computer systems at a reasonable cost. Atime-shared operating system uses CPU scheduling, and multiprogramming to provide each user with a smallportion of a time-shared computer. Each user has at least one separate program in memory, which is called aprocess. When a process executes, it generally runs for only a short time before it either finishes or needs toperform Since 1/0 typically takes place at human speed, which is incredibly slow as compared to the electronicspeed of the CPU, so the CPU is idle during the I/0 operation. Rather than let the CPU be idle, the operatingsystem will rapidly switch the CPU to the program code of the other user. As the system switches rapidly fromone user to another, each user feels as if the -@PU is dedicated to his program, whereas actually one CPU isbeing shared among many users.Real-Time SystemsA real time system is a special type of O/S and is used when fixed time-constraints for a processor response ordata output are defined. The system is used as a Control device in dedicated applications. If the system doesnot produce the required result within the pre-defined time-constraints, it fails. Real-Time systems are sensorcontrolled where in sensors provide data to the computer which is analyzed and controls are adjusted to modifysensor inputs. e.g. Industrial Control Systems, Weapon Control Systems, ROBOTICS, automobile fuel injectionsystems are real timeA real time system can be designed in two ways.(a) As a Hard real time system, which is completely time bound. In this type o system support features likeVirtual Memory etc. are missing and processing takes place in non-volatile memory or the Read Only Memory(ROM). This design differs from conventional OS design of time-sharing systems where H/W is separated fromuser by distinct levels of S/W.(b) As a Soft real time system which is like a time-sharing system. Here priorities are taken into considerationfor critical tasks to be completed but long waiting times are avoided. Since a soft real time system does notoperate in fixed time constraint so it is not used in critical applications like ROBOTICS or Industrial Control but isused in applications like Multimedia Design and Virtual Reality. In these systems advanced O/S features likeVirtual Memory need to be provided. Some latest versions of Unix provide real time operation features.“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 26