OPERATING SYSTEM (PART 2)

Usually different computers are dependent on a set of machine code that is standard and is different for different microprocessors. The operating system removes this difficulty and provides a set of standard commands to user, which are not machine dependent. Even though an operating system is usually invisible, it is essential for every computer system to have an operating system. The operating systems can be classified as:-

• Single User Operating Systems
• Multi User Operating Systems

The brief systems does the following jobs:-

• It provides an interface between the user and the computer
• It controls access to the machine
• It works with ROM to start up or "Boot" the computer
• It schedules on efficient use of the CPU while eliminating the need for human intervention
• It manages data and information in internal memory
• It manages files on secondary storage, making them available as needed while providing security to multiple user
• It provides a palte form to run other software programme
• It manages peripheral devices such as printer, disk drives, and tapes drives

A platform defines a standard for which software packages are developed to run. A platform is defined by two basic elements:-

1. The processor (for example intel Pentium or Power PC) and
2. The operating system (for example MS DOS or Windows)

Generally, software created to run on one platform is not compatible with any other platform and therefore cannot run on any other platforms.

A single system can however be configured to run under different platforms like MS DOS, Windows 98, 2000, 2007. The selection of a platform is important because it establishes boundaries for what you can and cannot do with your computer system. Before choosing a platform consider the following:

• Availability of oppropriate commercial applications software for the platform
• Compatibility of platform with existing hardware, software and expertise

SINGLE USER OPERATING SYSTEMS

Single user operating systems are used on individual systems or computer. This type of operating system is used only on personal computers or microcomputers and is installed on all individual machines. Each system is designed for a specific microprocessor. Some of the most widely used single user are:-

• MS-DOS or Microsoft DOS
• PC DOS
• Machintosh System
• DOS Shell
• OS/2
• Windows

All the above operating systems reside on disks and hence are called (DOS).

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WHAT IS OPERATING SYSTEM

A computer is a digital electronic device. Hence to perform vaoius operatings it can accept commands only in digital form. There is a need to have an organized collection of programme that controls the over all operations of a computer. Thus software that enables the communication between the user and the computer system as a whole is called an operating system. It interprets the users commands into a language which the machine can understand, and executes the instructions and helps the computer to handle vaious peripheral devices such as keyboard, monitor, floppy disk drive, hard disk drive, the printer and the other devices. For example, the operating system must monitor the keyboard to determine when a key has been pressed to provide input to the computer. It must also manage the monitor screen and printer to provide output from the computer. The operating system provides link between the user and the computer and enables the user to have complete control over the computer system by giving certain commands from the keyboard or any other input device. The operating system is a set of system programme, known as control programme or supervisor, which resides all the times in the memory (RAM) of a computer and controls all the comonents of a computer system as soon as computer is turned on. Through the use of operating system, the user delegates part of his burden of data processing to the computer itself to achieve high efficiencies of which the processing systems are capable.

FUNCTIONS OF THE OPERATING SYSTEM

According to the facilities provided by operating systems, these range from simple systems to complex ones. The philosophy underlying the operating system is that the computer should perform such jobs of an operator, which it can do faster and more accurately. The operating system remaining in the background performs tasks that are essential for the efficient functioning of the computer system such as:

• Controlling Basic Input and Output Devices
• Allocating System Resources
• Managing Storage Space
• Maintaining Security
• Detection of Equimpment Failure

Various types of operating system have been developed to provide the computer user with a workable system for different purposes such as multiprogramming, multiprocessing, batch processing, remote processing, etc.

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VARIETY OF SOFTWARES

Represents a recent entry into the prepackaged software race. As the name implies, integrated software packages combine or integrate, a number of individual software packages into a single larger programme having two types of integrating software

• Horizontal Integration and
• Vertical Integration

HORIZONTAL INTEGRATION

Describes the combination of application packages such as word processor, data manager, spreadseet and graphic pakcages into one pakcage that can share data. The ability to combine and pass data between application packages makes integrated software very useful.

VERTICAL INTEGRATION

Refers to the enhancement of a single package. For example adding a spelling programme dictionary or thesaurus to a word processor would be considered vertical integration.

BUSINESS SOFTWARE

A second major application software vategory, business software, helps organizations efficiently accomplish routine tasks. Often, buiness software is divided into two categories, horizontal market softwae and vertical market software. Horizontal market software refers to generic software packages that can be used by many different kinds of businesses. Accounting and payroll applications are good examples of horizontal market software. Every business needs to maintain a set of books to track income and expenses. Accounting software is designed to computerized the book keeping tasks typically required in most businesses. Almost every business has employees and needs to maintain payroll records. Payroll software keeps track of employee hours and produces the reports required by the government for income tax reporting.

ENTERTAINMENT SOFTWARE

Entertainment software is designed to entertain you. With entertainment software, you can play cards, fly a simulated jet, play 18 holes of golf, solve a Sherlock Holmes mystery, battle monsters, or explore nre worlds.

EDUCATION AND REFERENCE SOFTWARE

Education and reference software is designed to help you learn more about a particular tpoic. One type of education software called CAI (computer aided instruction), or tutorial software, can help you learn how to do things, for example, how to type, how to fix your car, how to use your word processor, how to speak French, or how to prepare for the GMAT exam. Educational simulations let you work with a computerized model of something in the real world, manipulate it, and see what happens. For example, some College and Universities use computerized simulations in introductory chemistry classes and students can experiment with chemical reactions without using real, and sometimes dangerous, mixtures. Reference software, such as electronic encyclopedias, can also help you lool up facts an any topic.

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WORD PROCESSING SOFTWARE

Helps your to produce documents such as reports, letters, papers and manuscripts. Word processing can involve a number of different activities, but generally these activities can be categorized as either text editing or print formating. In the text editing process, text is entered into the computer via a keyboard. You can edit your work using insert a deleted keys. You can also move text to improve the logical flow of concepts of you document.

The second category of word processing activity, print formating occurs when the word processor communicates with the printer through the computer system and tells the printer how to print the text. Some of the more common print formating features found in Word processors is margin settings, lines spacing, centering, automatic paging, character enhancements and headers and footers. Character enhancement features may allow the user to underline, italicizw, boldface, subscript or superscript tex within a document.

SPREDSHEET SOFTWARE

Helps you to work with numbers. An electronic spreadsheet is a computerized version of traditional spreadseet used by accountants for performing financial calculators and recording transactions. An electronic spreadsheet is a table of rows and cloumn used to store and manipulate any kind of numerical data.

The point shere a row nd a column meet is called a cell. Each cell is a unique location. You enter number and formula in the cells and the computer automatically performs the calculations.

DATABASE MANAGEMENT SOFTWARE

Helps you to work with facts and figures. Data managers are application software packages that computerize everyday tasks of recording and filing information. With data manager, data is recorded with the aid of a computer and is stored on the computer's secondary storage devices where it can accessed. They can be used to keep a personal property inventory, creating a list of important documents, creating a mailing list and keeping a computerized address book and phone listing. They offer a way to keep organized, readily accessible records.

GRAPHIC SOFTWARE

Draw a pictures, 3-D images and animatins. Graphic software allows you to convert data into meaningful diagram or graphs such as pie chart, graphs and bar charts, graphics software ranges from business to artistic user. If you have limited artistic ability, you can use graphic software to retrieve pre-drawn clip art images, which you can modify.

COMMUNICATION SOFTWARE

Allows your computer to talk to other computers. Communication software is the key that unlocks the door to a new world of information and information related services. With communication software, a microcomputer become more than a small stand alone computer. It becomes capable of interacting with a remote computer may be located in the next room of in New York. It provides you computerized mailbox that collects documents or mail you receive from other computers. It enables the transfer of files between a PC and another computer. It also allows you to send/receive faxes directly.

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APPLICATION SOFTWARE

System software performs essential support functions. Among these software products are operating systems, language translators, utility programms, performance monitoring programms.

However, application software also referred asproductivity software are developed to help the user to increase his/her productivity. Originally application software was developed by the organizations that owned computers. They have their own programmers to create programms according to their needs. Later, the companies that manufactured the computers began to develope and sell software packages along with their computers. These solutions packages were designed for the kinds of data management tasks that most organizations had, business related activities such as record keeping, inventory control, and payroll accounting.

Eventually, some firms began to sell software that deal with common computer tasks. There has been a tremendous increase in the use of application software packages with the development of microcomputers. Two factors are largely responsible:

1. The increased cost of developing one's application software.
2. The irse in the popularity of microcomputers.

Individuals and small businesses wanted specialized programms for creating letters and memos or for calculating their monthly budget. At first PC application programms were designed to create letters and memos and the electronic spreadsheet was created to manage numerical data. But as PC programmers deicovered new ways to use their computers, they began to design and sell an endless variety of specialized software for every type of computer user. Application programms are widely used for entering and editing text (Word processing desktop publishing programms) for entering and manipulating numeric data (spread sheet and many other business programms) and for record keeping (database management programms). These types of programms are sometimes called as general purpose applications.

Application software can be divided in four major classes. These are:

1. Productivity Software
2. Business Software
3. Education Software
4. Entertainment Software

PRODUCTIVITY SOFTWARE

The most important type of the application software is productivity software. It helps you to work most effectively. Productivity software includes:

• Word Processing Software
• Spreadsheet Software
• Database Management Software
• Graphic Software
• Cpmmunications Software and
• Integrated Software

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PROGRAMMING LANGUAGE TRANSLATOR

The earliest computers were programmed by arranging various wires and switches within the computer components. In the ENIAC, upto six thousand switches could be set to execute programmes. When a new programme was to be run, all the switches had to be rest. The EDSAC, the first stored programme computer allowed instructions to be entered into primary storage without switches having to be rewired or rest. Special codes that later becam known as machine language were used to enter the instructions. In the mid 1950s the development of FORTRAN signaled the beginning of a trned towards more sophisticated ways of giving computers instructions, these high level programming languages emphasized procedured and problem solving rather than the operation of the computer hardware. The lowest level language is machine language, the language of the computer. Machine language is the only language that a computer can recognize and act on directly. Machine language is the most efficient language that allows the programmer of fully use the computer's potential for processing data. But it is difficult for a programmer to learn and remember. Assembly languages were developed to overcome the disadvantages of machine languages. The programmer uses mnemonics instead of 1's and 0's to specify machine operations. The mnemonics are English like abbreviations for the machine language instructions. For example LDA stands for load in register A and STB stands for store in register B. Assembly languages programmes are highly efficient in terms of storage space use and fast processing. During the past fifty year nearly five hundred computer languages have been developed. These language have been categorized as Machine languages. Assembly languages and symbolic languages.

SERVICE SOFTWARE

Service programmes make life as a user a little easier. It can be further subdivided into

• Utlity Programms
• Library Programms
• Device Drivers

Hundreds of utility programms help us a better manage available hardware, software and data resources. Although an operating system usually works behind the scenes. there are times when you need utilities or utility software, to do things such as prepare disc to store data, detect computer viruses on a disc, prepare, copy, merge, sort out and update files. Protects monitor screen from burning during idle monitors by screen saver utility programme thus prolonging the life of monitor. A text editor utility programme such as Wrodstar, Wordperfect, Norton's editor etc., is used to create and modify a document another popular utility programme called data compression, help us reduce the size of a stored image/text for more efficient transmission over a data communication link.

Library programme maintains a directory of frequently used software module and their locations. These programmes migh consist of manufacturer supplied or user written routines or complete programms to computer mathematical functions such as root, exponential function and matrix inversion, control input/output devices, maintain appointments and so on. The library programms makes these routines available when requested by the user, the operating system or an application programme.

The type of programme require to run peripheral devices such as mouse, keyboard, floppy disk, CD-ROM modem, printer etc., reqire to install software that tells your computer how to use the device. This type of software is called device driver. When you purchase a hardware device, you also receive a disk containing a device driver.

A system programme may, for example allocate storage for data being entered into the system. The programme varies from computer to computer and cannot be used on different machines unless they are modified. System software is usually provided by the computer manufacturer or a specialized software developing firm.

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OPERATING SYSTEM

• Operating System
• Programming Language Translator
• Service Software

OPERATING SYSTEM

An operating system is a collection of system programmes that control and coordinate the overall operation of a computer system. These programmes act as an interface between the hardware and the applications software. It manages the resources of the computer namely the central processing unit, memory and input/output devices. Normally transparent to the user, operating system performs its task without intervention. The user is usually unaware that the operating system is quietly at work assisting the user in vaious ways. Examples are Disc operating system (DOS), Macintosh, and Unix. Dos is a command driven interface discussed in the next pages.

The trend today is towards more user friendly, graphics oriented environment called a graphic user interface (GUI), the user can interact with DOS through a series of pull down menu. Software that provides a GUI instead of command driven interface is called a shell. Dos shell provides a Graphical user interface (GUI) and was first introduced with DOS 4.0 version. Operating system 2 (OS/2) is an operating system devloped for IBM compatible microcomputers. UNIX is another operating system that was once used only on mini and mainframe computers, but has now been adapted for microcomputers as well. Unix is a protable multitask multi user, layered operating system. It is written in C language, which is a high level language. Hence it is less hardware dependent than those written in lower level machine language. ZENIX or XENIX is another operating system developed by Microsoft for microcomputers. It has multiprogramming capabilities with many useful utilities and GUI and is gaining rapid acceptance Windows is an operating system developed by Microsoft for microcomputers using Intel microprocessors. A true Windows operating system is Windows NT (New Technology). It is intended to work on computers for multiple manufacturers. Windows NT provides a whole new set of applications. Applications that once ran on large computers can now run under Windows NT on PCs. Windows NT can run any programme written for the earlier MS DOS, Windows, and OS/2 operating systems. Macintosh operating system is an operating system particularly used in Apple Computers. It has an extremely user friendly GUI.

continue..DOS, OS/2, IBM, UNIX, ZENIX, XENIX

COMPUTER SOFTWARE

COMPUTER SOFTWARE

A computer is the most versatile machine in the history that has ehanced the mental capability of human and has relieved him from mental labour. A computer can produce typeset documents, manipulate data, translate Japanese into English, compose music, design spacecrafts, control and regulate industrial plants, diagnose diseases produce piece of art, forecast weather, control flights, keep track of reservation, provide world wide data communication become partner to play games and much more.

All this versatility that a computer acquires is due to the software. Software can be as the driving force of computer without which it would be nothing except a well constructed combination of electronic device and circuits.

We interact with software to direct the overall activities within a computer. For example, if you wish to print a spreadsheet, you choose print command from your spreadsheep software's menu options. The print routine programme is executed, performing the internal operation needed to print your spreadsheet. Computer hardware is useless without software, that runs the computer for specific task. Similarly software is useless without hardware.

A computer programme is a set of detailed, step by step instructions tell a computer how to solve a problem or carry out a task. The step in a programme is written in a language that the computer can interpret or understand. It is the programme that controls the processing activities of a computer and tells the computer what to do and is referred as software. In order to produce useful output, the hardware and software must work together.

TYPES OF SOFTWARE

Software can be divided into two main groups:

• Sytem Software: Which coordinate the operation of the computer and helps the computer to carry out its basic tasks.
• Application Software: Which solve particular user problems and helps the user to carry out a task.

System Software and Application Software can be further subdivided into the following groups:

SYSTEM SOFTWARE

System software includes the programms that directly affect the operation of the computer. They are designed to facilitate the use of the hardware and to help the computer system run quickly and efficiently. They direct the fundamental operations of your computer such as displaying information on the screen, storing data on disks, sending data to the printer, interpreting the typed commands and communicate with peripheral devices. In addition system software provides a foundation so that application software operates correctly and use peripheral devices properly. System software can be divided into three main groups.

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BOOLEAN ALGEBRA

BOOLEAN ALGEBRA

A digital computer is made up of various types of simple circuits arranged and grouped according to the rules of symbolic logic. Logic is the science that establishes the validity of thought or reason. As a result of which what is true in one statement will be true in all equivalent statements Gottfried W. Leibnitz (1646 -1716) was the first who tried to develop a general method in which all truths of reason would be reduced to a kind of calculation. But the founder of symbolic logic was George Boole (1806 - 1876) who gave the world a form of mathematical logic now known as Boolean algebra. The significance of these developments was not realized at that time. Boolean algebra find its application to problems in the form of staements having answers either ture or false. It was the binary nature of these true/false problems which linked it with computer developments. The fundamental and simple ideas of logic outlined by Boole and his preducessors provide the foundation for many of the circuit applications in digital computer. But logical design is not limited to this area alone. The same principles have a direct bearing on and an increasing importance in control circuits for other electronic devices, such as digital watches, microwave oven, automatic cameras and instruments used for automatic control of manufacturing processor.

Blooean algebra like any algebra uses algebraic notation to express logical relationship in the same way that ordinary algebra is used to express mathematical relationships. In ordinary algebra an expression such as

x + y = a

consists of variables x, y and a which take numbers as values and symbols for mathematical operations such as (+) for addition. In Boolean algebra the same types of expression used are represented by set of elemetns, a set of operators and a set of rules satisfied by these two logical operators.

Since all electronic devices circuits have two discrete states ON and OFF. therefore we deal with two valued Boolean algebra.

A two valued Boolean algebra has a set with only two elements 0 and 1. A two valued Boolean algebra is also called switching algebra or binary logic. In our subsequent discussion we shall use Boolean algebra for two valued Boolean algebra.

ELEMENTS OF BOOLEAN ALGEBRA

In Boolean algebra an expression is constituted using constants and variables. Boolean Constants, Boolean variables.

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TYPES OF DATA

TYPES OF DATA

As we know that data means collection of facts, therefore, we need symbols for their representation. These symbols may be letters, words or figures. For example 3 books, 25 students, 23rd March, 40 Watt, PIA, 140847, each item conveys different meanings. In computers data items can be classified into following three types.

1. Numeric Date
2. Alphabetic Data
3. Alphanumeric Data

NUMBER SYSTEM

Digital computers are machines which responds numbers rather than letters. All the data and instructions must, therefore, be supplied in the coded numeral format. These numerals have specific meaning for computers. Thus number systems are very important to understand because the design and organization of a computer is dependent upon the number systems. The decimal system for counting has been so widely adopted that we rarely consider the possibilities of other number system. However, the binary number system, has proved the most natural and efficient system for machine use.

THE DECIMAL NUMBER SYSTEM

The decimal number system consists of 10 digits namely 0 to 9. A number written using these digits is called a decimal number. The value of each digits in a number depends upon the following:

• The face value of the digit, i.e. the digit itself
• The base of the system.
• The position of the digit in the number

THE BINARY NUMBER SYSTEM

In representing data by ON-OFF switch position there are only two possibilities and the corresponding numbers are 1 and 0. Binary number system is a very important number system so far as the digital computers are concerned. The binary digits are abbreviated to BITS. The word BIT stand for either of the binary digits 0 or 1. Since the system has only two digits, therefore, in the binary system the base is 2. Thus all the numbers in the binary system are written with the help of the digits 0 and 1. The positional value or place value of each digit.

NUMBER CONVERSION

Human normally deals with decimal number system while binary is needed for porcessing in digital computers other number systems are used for coding and storage purposes. Thus inter-conversion of number from one number system into other number system becomes important for compulation and data processing in digital computers.

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DATA REPRESENTATION AND INFORMATION

DATA REPRESENTATION

The most striking feature of a digital computer is its gnerality. It can follow a sequence of instructions, called a programme that operates on a given data. The user can specify and change programme and/or data according to the specific need. As a result of this flexibility, general purpose digital computers can perform a wide variety of information processing jobs. The effectiveness of computers and the potential benefit to society lies in their versatility and processing speed. Digital computers have made possible many scientific, industrial and commercial advancements which otherwise would have been unattainable.

Digital computers are the machines which responds numbers rather than letters. All the data and instructions must, therefore, be supplied in the coded numeral format. These numerals have specific meaning for computers. Thus number system are very important to understand because the designe and organization of a computer is dependent upon the number systems. The decimal system for counting has been so widely adopted that we rarely consider the possibilities of other number system. However, the binary number system, has proved the most natural and efficient system for machine use.

Computer are often called data processors. The numbers, facts, names etc, that are represented by symbols. The symbols may be printed characters. Since computeris a physical device, the symbol it handles must be in some physical form. In the abacus numbers are represented by the position of beads, we assign a number to a bead. In this way we represent a particular number. Digital compurters are built from components that have two states ON and OFF like electric switches.

DATA AND INFORMATION

The term we use to describe the signals with which computers work is data. The word data and information are often used interchangeably. There is an important distinction between them. Data is the words, numbers and graphics that describe people, events, things and ideas. Data becomes information when you use it as the basis for initiating some action or for making a decision. Information then is defined as the words, numbers and graphics used as the basis for actions and decisions. A representation of facts, concepts or instructions in a formalized manner suitable for communication, interpretation or processing by humans or machines is called data. In short data means collection of raw facts.

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FIXED MAGNETIC DISKS (HARD DISKS)

FIXED MAGNETIC DISKS (HARD DISKS)

The increasing complexity of the software requires additional storage space. The user must switch floppies in and out as by the software packages. To meet this growing need for large secondary storage, the hard disks are developed. Hard disks or fixed disks, also called winchester, are premanently installed or fixed within the system unit. All fixed disks are rigid are usually made of aluminum with a surface coating of easily magnetized elements, such as iron, cobalt. Chormium or nichel a fixed disks or hard disk is a high speed, target capacity disk and is referred as a mass-storage magnetic medlum that provides computer system with the ability to read or retrieve large amount of information swquentially or randomly under the direction of a controller board. A hard disk contains several disk platters stacked on a single rotating spindle. Data are stored on all reconding surface.

For a disk with four platters, there are eitght recording surfaces on which data can be stored. The disks spin continuously at a high speed (from 3600 rpm to 6000 rpm high speed) within a sealed enclosure. The enclosure keeps the disk-face surface free from contaminations, such as dust and cigarette smoke. This contamination-free enviironment allows hard disk to have greater density of data storage than the interchangeable diskettes. In contrast to a hard disk, a diskette is set in motion only when a command is issued to read from or write to the disk. An indicator light near the disk drive is illuminated only when the floppy diskette is spinning.

COMPACT DISK

Compact disk read only memory. Systems are becoming popular, especially for use with microcomputers. These systems use a disk that is less than 5 inches in diameter and yet can hold more than 600 megabytes of data. Although these disks look just like the well known music CDs, they are used to store the kind of digital information used in computers.

The large colour graphic and video image files that are used with multimedia are often stered on optical disks. In addition, these disks can store two channels of sound just like the popular music CDs. Infact, a computer controlled CD-ROM drive can be used to play the two music channels on a standard music CD, and CD-ROM disks are now available with both the music and comuterized information about the music.

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SEQUENTIAL ACCESS, DIRECT ACCESS STORAGE

SEQUENTIAL ACCESS

Access through sequential access storage is non-addressable that is an operator cannot refer directly to the contents of a particular storage location such as that used with magnetic tape. This involves examining sequentially all recorded data. This form of storage necessitates tape searching by starting at the beginning of the tap and continuing to search through all records until the desired information area in found.

DIRECT ACCESS STORAGE

Direct Access Storage is addressable that is a given item can be selected from any where in storage by simply specifying the address where it is located Direct Access devices such as magnetic disks provide immediate access to individual records and do not require reading from the beginning of a file to find a particular record.

Auxiliary storage is also called the backing storage because it is used to supplement the capacity of main storage. Backing storage is essential not only due to the limited size of the random access memory (RAM) but also because RAM is only a temporary memory and moreover it is expensive a well. Auxiliary storage provides massive capacity for storing large number of programme and vast amount of daa of the order of hundreds of megabytes. Hence the name mass storage is also given to backing storage. These permanent storage devices come in the following forms:

• Magnetic Tapes
• Magnetic Disks
• Laser Holographic Storage

MAGNETIC TAPE DEVICES

A popular form of secondary storage for both mainframe and personal computers is magnetic tape. Megnetic tape is a thin Mylar tape from 1/4 inch to 1 inch wide. The tape is coated with ferrous oxide, on which information is recorded in binary form. Magnetic tape is available in two primary forms, reel-to-reel tap and data-cassett/cartridge tape.

The information is transferred to from the tape with a read/write head, which encodes the magnetic signals on the ferrous oxide tape coating as the tape moves across the read/write head. Most computer centers have a tape library run by special librarian who manages tape storage. These tapes are cheap and reliable but they take considerable time to load and to loacte a programme.

MAGNETIC DISKS

A magnetic disk is a metal or plastic disk coated with ferrous oxide. A bit pattern may be magnetically coded onto the ferrous oxide. Because these disks spin in the disk drives, the read/write heads can reach any data on the disks directly rather than sequentially. Because of its random and sequential processing capabilities, magnetic disk storage is the overwhelming choice of computer users. A variety of magnetic disk drives (the hardware devices) and magnetic disks (the media) are manufactured for computer use. There are two fundamental types of magnetic disks, interchangeable disks calles the floppy disks and fixed disks called the hard disks.

Nearly all PCs sold today are configured with at least one fixed disk drive and one interchangeable disk drive. Having two disks increases system flexibility and throughput. The interchangeable disk drive provides a means for the distribution of data and software and for backup and archival storage. The high capacity hard disk storage has made it possible for today's PC users to enjoy the conenience of having all data software readily accessible at all times.

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FLASH & CACHE MEMORY, SECONDARY MEMORY

FLASH MEMORY

Flash memory is a type of non-volatile memory that can be altered easily by the end user. Flash memory is a feature of many new I/O and storage devices. The intelligence of these devices can be upgraded by simply downloading new software from a vendor-supplied disk to flash memory. Upgrades to early inptu/output and storage devices required the user to replace the old circuit board or chip with a new one. The emergence of flash memory has eliminated this time consuming and constly method of upgrade. Look for non-volatile flash memory to play an increasing role in computer technology as its improvements continue to close the gap between the speed and flexibility of CMOS RAM.

CASHE MEMORY

Cashe Memory Proramms and data are loaded to RAM from secondary storage because the time required to access a programme instruction or piece of datum from RAM is significantly less than from secondary storage. Thousands of instructions or pieces of data can be accessed from RAM in the time it would take to access a single piece of datum from disk storage RAM is essentially a high speed holding area from data and programms. Infact, nothing really happens in a computer system until the programme instructions and data are moved from RAM to the processor. This transfer of instructions and data to the processor can be time consuming, even at microsecond speeds. To facilitate an even faster transfer of instructions and data to the processor, some processors are designed with cache memory. Cache memory is used by computer designers to increase computer system throughout. Throughout refers to the rate at which work can be performed by a computer system.

Like RAM, cache is a high speed holding area for programme instructions and data. However, cache memory uses a technology that is about 10 times faster than RAM and about 100 times more expensive. With only a fraction of the capacity of RAM, cache memory holds only those instructions and data that are likely to be needed next by the processor.

SECONDARY MEMORY

Secondary memory, or Secondary storage is memory also referred as backing storage is used to supplement the capacity of main storage. This memory stores a bulk of information. It is also called auxiliary storage or mass storage. The information stored in this memory is used by the CPU by first bringing it to main memory. Examples of auxiliary memory are magnetic disks, magnetic tape and mass cartridge systems. Auxiliary storage is of two types: Sequential and Direct Access.

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SIMMs and DIMMs & READ ONLY MEMORY (ROM)

SIMMs and DIMMs

The capacity of RAM in a computer affect computer's power. More capacity of RAM means the computer can use larger an more powerful programms and those programms can access bigger data files. More RAM can make computer run faster. The computer does not necessarily have to loa an entire programme into memory to run it, but the more of the programme it can fit into memory, the faster the programme will run. For example, a PC with 8 MB of RAM is capable of running Microsoft Windows even though the programme actually occupies about 40 MB on the disk storage space. When you run Windows, the programme does not to load all the files of windows into memory to run properly. It load only the essential parts into memory. When the computer needs to access other parts of the programme on the disk, it can unload nonessential part from RAM back to the hard disk and load the programme code or data it needs. However if your PC has larger RAM, windows will run faster because CPU will need to unload programme instructions between RAM and the hard disk less often.

Instead of (dual in line Pin) DIP package, today's computers use SIMMs (Single in-line Memory modules) and plug it in your computer easily. SIMMs and DIMMs provide large memory capacity but require very little space. They are available in many several configurations and in variety of speed. Each SIMMs or DIMMs can hold 4 MB to 128 MB of RAM. You can expand RAM capacity of your computer by plugging in more SIMMs or SIMMs chips.

When you purchase additional memory for your computer, you must make sure that the memory modules you purchase are the current type, and sould match with the configuration and speed for your computer system.

READ ONLY MEMORY (ROM)

A special type of internal memory contained in the computers is the Read Only Memory (ROM). This is a permanent of the computer designed by the manufacturers of the computers and cannot be altered by the programmer. The contents of ROM, a non-volatile technology, are hard wired (i.e., designed into the logic of the memory chip) by the manufacturer and can be read only. It is used to store the instructions required to control the basic input outpur operations of a computer whenever the computer system is turned on when you turn on a microcomputer system, a programme in ROM that resides in it automatically readies the computer system for use and displays the initial display-screen prompt. ROM is a semiconductor chip programmed at the time of its manufacture and is not reprogrammable by the user. Programmes sotred in ROM are called firmware. ROM is a non-volatile memory, i.e. the contents of this type of memory are not lost when the computer is turned off.

A variation of ROM sis programmable read-only memory (PROM). FROM is ROM into which you, the user, can load read-only programms and data. Some microcomputer software packages, such as electronic spreadsheets, are available as PROM units as well as on interchangeable disks. Generally, once a programme is loaded to PROM, it is sel-dom, if ever, changed. ROM and PROM are used in a variety of capacities within a computer system.

MAIN & RANDOM ACCESS MEMORY (RAM)

MAIN MEMORY

Main memory is the computer's primary storage. It is an extenstion of the Central Processing Unit (CPU) and is directly accessible to it. Its function is controlled by the Control Unit (CPU), which sends READ or WRITE signal for the appropriate memory location. Main memory accepts data and instructions from the input unit, exchanges data with the supplies instructions to other parts of the Central Processing Unit (CPU). This memory unit also stores those instructions and data, which are currently being used by the CPU or those instructions and data, awaiting immediate execution. Its capacity must be sufficient to retain both the usable amount of data and instructions needed for processing it. Some operations require more instructions or data than can be held is main memory at one time. In such cases, main memory is supplemented with auxiliary storage.

The capacity of a storage device is expressed as number of bytes, characters or bits. One byte is a group of eight bits that forms one character. Thus if the memory of a computer is 32000 bytes, it means that it can sote 32000 characters. Semiconductor storage (intergrated circuits) and magnetic cores are the most widely used forms of main storage.

Besides reduced size increased speed, semiconductor storage offers the advantage of non-destructive read. There are various storage types available, which include RAM, ROM, PROM, EROM, and EAROM. The most common kind of semiconductor storage is RAM (Random Access Memory) and ROM (Rad Only Memory).

RANDOM ACCESS MEMORY (RAM)

RAM is a memory in which each element of information has its own address (location) and from which any element can be retrieved easily and quickly by using that address. It is a temporary memory of a computer used to store the data and the instructions of the user when the computer is on. It is also called as Read-And-Write Memory (Ram) since the computer can store (write) data at any selected location (address) and at any subsequent time, retrieve (read) the data. The contents are lost when the power to the computer is shut off. Thus RAM is active only when computer is on and also referred as a volatile memory because the data stored in it disappears whenever he computer is switched off. However the RAM has the advantage of much better access time, higher transfer rate and simple interfacing. Generally RAM is meausured in K bytes or M bytes. Large RAM sizes provides larger amount of information which a computer can hold for processing and hence increases the processing speed.

Unlike magnetic secondary storage devices, such as tape as disk, RAM (primary storage) has no moving parts. RAM, a read-and write- memory, enables data to be both read and written to memory. Data can be accessed from RAM without any mechanical movement at electronic speed, close to the spee of light. Most of today's computers use CMOS (Complementary Metal-Oxide Semiconductor) technology for RAM. A CMOS memory chip less than one fourth the size of a postage stamp can store more than 4,000,000 bits, or more than 400,000 characters of data. Physically, memory chips are installed on single in-line memory modules or SIMMs. SIMMs are circuit boards with links directly to the processor.

The most common RAM technologies are dynamic RAM (DRAM) and static RAM (SRAM). DRAM is used in more computer than SRAM. However, SRAM is faster than DRAM because it does not have to be refreshed hundreds of time a second like DRAM. It is also much more expensive and requires more space and power than does DRAM.

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LASER HOLOGRAPHIC, STORAGE DEVICES

LASER HOLOGRAPHIC STORAGE

With recent advances in holography and laser beam technology, computer developers are studying optical memories with capacity greater than 100 megabits of data and random access time may be as short as one microsecond. Hologrammes make use of high-energy laser beam to store or display three dimensional images. The image produced by a hologram can easily be read by a photodetector, and information can be stored.

A holographic memory is made on a special recording medium similar to photographic film. Information is retrieved from the memory by projecting the data recorded on the hologram onto a light sensitive detector. The detector converts the optical information into electronic signals that computer can process.

STOREAGE DEVICES

Computer storage also referred as computer memory is actually an electronic file in which instructions and data are placed until needed. Computer storage is divided into two classes:

1. Main Storage or Main Memory
2. Secondary Storage or Secondary Memrory

MEMORY UNITS

The capacity of a storage device is expressed as number of byties, characters or bits. One byte is a group of eight bits that one character. Thus if the memory of a computer is 32000 bytes, it means that it can store 32000 characters.

BITS AND BYTES

The basic unit of a digital computer is a bit, which stands for binary digit. A bit is binary number and has value1 or 0 representing ON or OFF state. In microprocessor, bits are grouped into set of eight, called a byte, a four-bit sequence is called a nibble. The memory of a computer can be thought of cells. Each of these cells contains one bit of information. Each cell will have either 0 or 1 state. The combination of eight such cells forms one byte. Each byte contains one character sucl, as A, B,......etc. A group of bits representing data or instruction that form the basic information unit of the computer is called a "word". A word may have a length of 8 bits, 16 bits, 32 bits or more. Thus a word of 16 bits size can be called as 2-byte word. Generally computers that handle larger words are considered to be more powerful than the computer that use smaller word sizes because greater amount of information can be processed in a single cycle. The storing capacity of a computer is measured in bytes. The basic unit of information in digital computers is a bit, which stands for binary digit. A bit is binary number and has value1 or 0 representing ON or OFF state.

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