1st Year Computer Notes CH#06 Computer Software and Programming Languages

Computer Software and Programming Languages


An information system has five parts. People, procedures, software, hardware and data. Software which is one of the most important part of an information system. Is an other name for a program or programs. Program is the step by step instructions that tell the computer how to do its work. The purpose of a software is to convert data (unprocessed facts) into information (processed facts). In most cases, words software and programs and interchangeable.

There are two major kinds of software-application software and system software.

Application software are the software the users of the computer use. Whereas system software are used by the computers.




Application Software

Application software may be describe as end-user software. They perform useful work on general-purpose tasks such as word processing and cost estimating.

Application software may be

1. Packaged

2. Custom Made


1. Packaged Software

Packaged Software are the programs prewritten by professional programmers that are typically offered for sale.


2. Custom-Made Software

Custom-Made or Custom programs are the programs written for a specific purpose and for a specific organization. Using computer languages, programmers create this software to instruct the company's computer to perform whatever tasks the organization wants.

There are certain general purpose programs which are called "basic applications" The most popular basic tools are


Word Processing Programs used to prepare written document.

Spreadsheets Programs used to analyse and summarize numerical data.

Database Manageers used to organize and manage data and information.

Presentation Graphic Programswhich are used to communicate a message.

Personal Information Management Programs used to organize and schedule activities.

Integrate Programs which combine some or all of these applications in one program.


Summary of Basic Application Software

The summary of the basic application software mentioned above has been given below. Which shows various software designed by well known software publishers. Microsoft, Lotus and Corel.


Basic Applications

Word Processors = Microsoft Word, Lotus, Word Pro, Corel WordPerfect

Spreadsheets = Microsoft Excel, Corel Quattro Pro, Lotus-2-3

Database Managers = Microsoft Access, Corel Paradox, Lotus Approach

Presentation Graphics = Microsoft PowerPoint, Corel Presentation

Personal Information managers Microsoft Outlook, Lotus Organizer

Integrated Packages = Microsoft Work, Lotus Works.

Software Suites = Microsoft Office 97, Corel Office 97


Common Features of Basic Application

As all the above mentioned categories of software are designed to be used by many people to perform most common kinds of tasks we call them basic applications. Most common application software have some common features. The most important of them are given below.


Menu

Almost all software packages have menus to present commands. Typically menus displayed in a menu bar at the top of the screen when one of the item is selected a pull down menu appears.

This is a list of commands associated with the selected menu.


Shortcut keys

Many applications also have shortcut keys for frequently used commands. Many of the shortcut keys are function keys. F1, F2 and so on. Others shortcut use key combinations typically consisting of the Alt, Ctrl or Shift key used in combination with a letter number or function key. For example in Word97 the short cut key F7 starts the spelling tools and the key combinations of shift and F7 starts the Thesaurus tools.


Toolbars

Toolbars are typically below the menu bar. They contain icons or graphic representations for commonly for commonly used commands.


Help

For most applications packages one of the menus on the menu bar is Help. This typically include a table of contents a search feature to locate reference information about specific commands and access to specific learning features such as tutorials and step-by-step instructions.


Dialog Boxes

Dialog boxes frequently appear after selecting a command from a pull down menu. These boxes are used to specify additional options.


Scroll Bars

Scroll bars are usually located on the right and / or the bottom of the screen. They enable user to display additional information not currently visible on the screen.


Edit

The ability to change or edit entries is a feature common to almost all applications. The edit feature makes revising and updating easy and is one of the most valuable features.


Save and Print

Common to all applications software is the ability to save or store your work as a file on a floppy or hard disk. This allows user to open and use the file at a later time in case user wants to add or modify the document. In addition all applications allow user to a copy of his document on paper.

Word processing programs and spreadsheets program are most commonly used categories of application software hence we explain them in much more detail.


Word Processors

word processing software creates text-based documents such as letter, memos, term papers and reports. Once it was thought that only secretaries would use word processors. Now they are used extensively in managerial and professional life. Indeed, it has been found that among the basic software applications. Word processors are most important software used by common people.

Popular word processing packages include Microsoft Word. Corel WordPerfect and Lotus Word Pro as shown in the above summary of basic applications.


Important Features of Word Processors

Some important features shared by most word processors are as follows


Word Wrap and the Enter Key

One basic word processing feature is word wrap i.e. word processor automatically moves the insertion point to the next line once the current line is full. The begin a new paragraph or to leave a blank line Enter key is pressed.


Spelling and Grammar Checkers

Many word processors include a spelling checker feature that identifies typing errors. For example Word97 identifies misspelled words with a red wavy underline. Similarly grammar checkers can be run that will identify poor wording excessively long sentences and incorrect grammar.

Alignment

Text can be aligned within the margin in various way. The most common alignment is left alignment.


Formatting

Text can be enhanced in a variety of ways including adding basics formatting such as bold, under line and italics.

Besides above mentioned feature other common features of word processors are References, Search and Replace, Tables, Hyperlinks, Thesaurus, Graphics, Internet publishing and Workgroup.


Spreadsheets

Spreadsheets is an electronic worksheet used to organize and manipulate and display option for "what-if" analysis. Spreadsheets are used by financial analysts, accountants, contractors and other concerned with manipulating numeric data.

Popular spreadsheets packages include Microsoft Excel, Quattro Pro and Lotus 1-2-3 as shown by above summary.


Common feature of Spreadsheets

Like the word processors, spreadsheets designed by various software publishers share following common features.


Formulas and Functions

Formulas are the instructions for calculations. They calculate result using the numbers in reference cells. Whereas functions are prewritten formulas that perform calculations automatically.


Analysis

The recalculation feature can be used to analyze the effect of changes to the spreadsheets.


Analytical Graphs

To help visualize the data in spreadsheets user can create analytical graphs or charts.


Workgroup

One of the newest additions to spreadsheets applications is the workgroup program which allows multiple users to collaborate electromically on spreadsheet.


Linked Files

Most spreadsheets programs allow users to link cells in one worksheet file to cells in other worksheets in the same file or to other worksheet files. Whenever a charge occurs in one file the linked cells in the other worksheets are automatically updated.


Advanced Application Programs

Besides above mentioned basic application programs there are certain programs which are called "advanced applications". These are more specialized than the basic application. These programs are widely used in certain career areas. The most popular tools are:


Graphic Programs used to create professional publications and to capture and edit graphic images.

Multimedia used to integrate all kinds of information including video, audio, graphic and text into a single interactive presentation.

Web Publishers used to create interactive multimedia web page. Project management used to plan projects schedule people and control resources.


System Software

The user interact with the application software whereas system software enables the application software to interact with the computer hardware. System software is a "background" software. It includes programs that help the computer manage its internal resources.


Kinds of System Software

System software deals with the physical complexities of how the hardware works. System software consists of the following four programs.

1. Bootstrap loader

2. Diagnostic routines

3. Basic input-output system

4. Operating System


1. Bootstrap loader

The bootstrap loader is a program that is stored permanently in the computer's electronic circuitry. When computer is turned on the bootstrap loader obtains the operating system from hard disk and loads it into memory. This is called booting the system.


2.Diagnostic Routines

These are also programs stored in the computer's electronic circuitry. They start up when machine is turned on. They test the primary memory the central processing unit and other parts of the computer. Their purpose is to make sure the computer is running properly.


3. Basic Input-Output System

It consists of service programs stored in primary storage. These programs enable the computer to interpret keyboard characters and transmit them to monitor or to a floppy disk.


Operating System

The operating system is a collection of programs that help the computer to manage its resources. The Operating System takes care of lot of internal matters. For example it interprets the commands user gives to run programs. It manages memory data and file.

The most important system program is the operating system which interacts between the application software and the computer. The operating system handles such details as running (executing) programs, storing data and programs and processing data.

Microcomputer operating systems change as the machines themselves become more powerful and outgrow the older operating systems.

The most popular microcomputer operating systems are

DOS the original operating system for International Business Machines (IBM) and IBM compatible microcomputers.

Windows not an operating system but an environment that extends the capability of DOS.

Windows 95 a widely used operating system with the built-in internet support.

Windows 98 a new operating system with the intensive internet and multimedia support.

Windows NT a powerful operating system designed for powerful microcomputers.

OS/2 Warp the operating system developed by IBM for powerful microcomputers.

Macintosh Operating System the standard operating system for Apple Corporation's Macintosh computers.

Unix an operating system originally developed for microcomputers that can run on many of the powerful microcomputers.


Disk Operating System

DOS's original developer Microsoft Corporation sells it under the name MS-DOS. It was originally standard operating system for all microcomputers which were IBM compatible or DOS based.


Advantages

1. Even today DOS is still widely used operating system.

2. An enormous number of application programs have been written for DOS. Indeed more specialized software is available for DOS for than any other operating system.

3. DOS runs on many computers, old and new that are cheap.


Disadvantages

1. It can support very limited primary storage.

2. It can be used only for single-tasking and not for multi-tasking.

3. It uses character-based interface.


Windows 98

Windows like Windows 95, Window 98 and Windows NT is not a operating system, rather an operating environment. While Windows 95, Windows 98 and Window NT are operating systems. But Windows 98 is one of the most popular operating systems being used nowadays. It is an advanced version, designed for today's very powerful microcomputers.


Advantages

1. It is faster in many common tasks like starting up loading applications and shutting down. It includes a Tune-up wizard automatically monitors system operation and suggest ways to improve performance.

2. Windows 98 is fully integrated with Microsoft's browser, Internet Explorer, making Internet access easier and faster.

3. Plug and play capability is extended to support the newest advance in technology. Multiple views of an application or multiple applications can be viewed on separate monitors simultaneously.

4. Windows 98 has advanced audio and video capability. With a tuner card, TV on microcomputers monitor can be watched.

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Disadvantages

1. Windows 98 requires at least a Pentium Microprocessor to operate effectively. Besides more hard disk space and memory are necassary.

2. Fewer applications have been written specifically for it. It can however run most DOS, Windows and Windows 95 applications.


COMPUTER LANGUAGE

Language is a system for representation and communication of information or data. Like human beings, a language or signal is required to communicate between two persons. Similarly, we cannot obtain any result by computer without langtage. Computer does not understand directly what we are communicating with computer as English or Arabic, it understands only machine language (binary codes 0-1). Computer translates English language into machine codes through interpreter then process instructions and give us the results.

The computer languages can be divided into two main levels.

* Machine language (0-1)

* Symbolic language (A-Z)

Symbolic languages are further divide into two main levels

* High-level language

* Low-level language


MACHINE LANGUAGE

Although computers can be programmed to understand many different computer language. There is only one language understood by the computer without using a translation program. This language is called the machine language or the machine codes. Machine codes are the fundamental language of the computer and is normally written as strings of binary 0-1.


ADVANTAGES AND LIMITATIONS OF MACHINE LANGUAGE

Programs written in machine language can be executed very fast by the computer. This is mainly because machine instructions are directly understood by the CPU and no translation of program is required.

However, writing a program in machine language has several disadvantage.
MACHINE DEPENDENT

Because the internal design of every type of computer is different from every other type of computer and needs different electrical signals to operate. The machine language also is different from computer to computer.
DIFFICULT TO PROGRAM

Although easily used by the computer, machine language is difficult to program. It is necessary for the programmer either to memorize the dozens of code number for the commands in the machine’s instruction set or to constantly refer to a reference card.
DIFFICULT TO MODIFY

It is difficult to correct or modify machine language programs. Checking machine instructions to locate errors is difficult as writing them initially.

In short, writing a program in machine language is so difficult and time consuming.


SYMBOLIC LANGUAGES

In symbolic languages, alphabets are used (a-z). symbolic languages are further divide into two main levels.

* High level languages

* Low level languages


LOW LEVEL LANGUAGE

A language which is one step higher than machine language in human readability is called Assembly Language or a low-level language. In an assembly language binary numbers are replaced by human readable symbols called mnemonics. Thus a low-level language is better in understanding than a machine language for humans and almost has the same efficiency as machine language for computer operation. An assembly language is a combination of mnemonic, operation codes and symbolic codes for addresses. Each computer uses and has a mnemonic code for each instruction, which may vary from computer to computer. Some of the commonly used codes are given in the following table.
COMMAND NAMEMNEMONIC

Add - ADD

Subtract - SUB

Multiply - MUL

Compare Registry - CR

Compare - COMP

Branch Condition -BC

Code Register -LR

Move Characters -MVE

Store Characters -STC

Store Accumulator - STA

An assembly language is very efficient but it is difficult to work with and it requires good skills for programming. A program written in an assembly language is translated into a machine language before execution. A computer program which translates any assembly language into its equivalent machine code is known as an assembler.


HIGH – LEVEL LANGUAGE

A language is one step higher than low-level languages in human readability is called high-level language. High – level languages are easy to understand. They are also called English oriented languages in which instruction are given using words. Such as add, subtract, input, print, etc. high level language are very easy for programming, programmer prefer them for software designing that’s why these languages are also called user’s friendly languages. Every high level language must be converted into machine language before execution, therefore every high level language has its own separate translating program called compiler or interpreter. That’s why some time these languages are called compiler langauges. COBOL, BASIC, PASCAL, RPG, FORTRAN are some high level languages.


INTERPRETER

An interpreter is a set of programs which translates the high-level language into machine acceptable form. The interpreters are slow in speed as compared to compilers. The interpreter takes a single line of the source code, translates that line into object code and carries it out immediately. The process is repeated line by line until the whole program has been translated and run. If the program loops back to earlier statements, they will be translated afresh each time round. This means that both the source program and the interpreter must remain in the main memory together which may limit the space available for data. Perhaps the biggest drawback of an interpreter is the time it takes to translate and run a program including all the repetition which can be involved.


Compiler

A compiler converts the programmer's procedural language program called the source code into a machine language code which is called the object code. This object code can then be saved and run later. Example of precedural languages using compilers are standard versions of Pascal, COBOL, and FORTAN.


Pascal

Another language that is widely used on microcomputers and easy to learn is Pascal, named after Blaise Pascal, a French mathematician. This language has become quite popular in computer science educational programs.


C/C++

C is general purpose language that also works well with microcomputers. It is useful for writing operating systems, spreadsheets programs, database programs and some scientific applications. C++ is a version of C that incorporates object-oriented technologies.


COBOL

COBOL which stands for Common Business-Oriented Language is one of the most frequently used programming languages in business. Through harder to learn than BASIC its logic is easier to understand for a person who is not a trained programer.


FORTRAN

Short for FORmula TRANslation, FORTRAN is a widely used scientific and mathematical language. It is very useful for processing complex formulas. That's why many scientific and engineering programs have been written in this language.

1st Year Computer Notes CH# 05 Input Output and Storage Devices

Input Output and Storage Devices


INPUT DEVICES

Input devices are used to provide data or information to the computer. The computer follows the instructions given to it by and input device. A variety of input devices are used with the computer depending on the type and purpose of input information. For example, a keyboard is commonly used to transfer data or information from human readable form to machine readable form. Other examples of input devices are: mouse, joystick, trackball, light pens, digitizers, scanners, optical character reader (OCR), touch window, etc.


MOUSE

The mouse is an input device that usually contains one or two buttons. As a user moves the mouse on a flat surface, the mouse controls the cursor movement on the screen. When the user presses one of the buttons, the mouse either marks a place on the screen or makes selection from data or menu on the screen. A mouse has a sphere on its underside. This rotates as the mouse is moved along a flat surface.

The mouse translate the direction and speed of rotation into a digital signals that identifies the position or control, the cursor on the computer.

A mouse can be used for many application, ranging from games to drawing and designing products with computer graphics. It provides an alternative for people who are uncomfortable with a keyboard but it also can be used in combination with a keyboard to input data.


TRACKBALL

A Trackball is a pointing device almost like a mouse turned upside down. The user controls the cursor on the screen by rolling a plastic ball with a fingertip or wrist. To execute commands with a Trackball, one or more buttons are pressed, much in the same way as is done with a mouse. The cursor can be moved around on the screen by rolling the ball with a thumb or finger.

Trackball is popular among users of laptop computers when space is limited and may be mounted on either side of the keyboard. For handicapped people who may have difficulty pressing keys on a standard keyboard or using a mouse, the trackball may be the answer since it edoes not require to moves the entire arm to use it.


SCANNER

Scanner is an input device. It is also called Optical Reader or Digital Scanner. It scans or reads text and picture printed on a paper and enters them directly into the computer memory.

The advantage of a scanner is that the user needs not type the input data in. This is a lust and accurate method for entering data into the computer. The scanner takes electronic images, of text or pictures from the paper it breaks each image into light and dark dots and stores them into the computer memory in machine codes. Scanned text can be edited by OCR software. Optical Character Recognition (OCR) software translates the scanned document into text that can be edited.

The image scanner is useful because it translates printed images into an electronic format than can be stored in computer's memory. The stored image can be transferred into a paint program or directly into a word processor. You can use software to organize and manipulate the electronic image.

KEYBOARD

A keyboard is the most commonly used input device which helps us in simply keying in required information in a computer. This information is subsequently stored in the computer’s memory. A keyboard can be used effectively to communicate with the computer but considered to be relatively slow as compared to other input devices. The keyboard is divided into following divisions:
ALPHABETIC KEYPAD

These keys are similar to a standard typewriter and is used to type general information.
NUMBERIC KEYPAD

These keys are used to input numeric data only. These are very useful in case of large numeric data input because all numeric keys can be accessed by one hand only. These keys can also be used as an alternative to the screen navigation and editing keys.
FUNCTION KEYS

These are keys marked as F1 - F12, located normally at the top of the keyboard. These are special keys provided to a programmer which allow him to attach special functions to each key. Each of these function keys are also given some special function in different packages.
SCREEN NAVIGATION AND EDITING KEYS

These keys are provided to move around in the screen. May programs use these keys to let the user move around the screen display. In some keyboards these keys are also provided inside the numeric keypad as alternate keys.

The description of commands assigned to function keys under the BASIC mode.

F1 - LIST Function - Used to display the lines of your program on the screen.

F2 - RUN Function - Used to execute a program from its beginning.

F3 - LOAD Function - Used to read a program from a storage device and store it in main memory.

F4 - SAVE Function - Used to store a program on a storage device from Memory.

F5 - COUNT Function - Used to restart a program after it has temporarily interrupted by a stop or CTRL + BREAK.

F6 - LPT1 Function - Used to transfer data from the video screen to the line printer.

F7- TRON Function - Refers to "trace on". This function causes the line number of program line to be displayed as these lines are executed.

F8 - TROFF Function - Refers to "trace off". This function cancels TRON function.

F9 - KEY Function - Use to change the function of the other function keys.

F10 - SCREEN Function - Used to return program to the character mode from the graphic mode and a;so to turn off the colour.


OUTPUT DEVICES

An output device is used to display the data or information that we receive from the computer. An output device can be used to display or print the intermediate or final results performed by computer. A variety of output devices are used with computer. The use of these devices depends on the type and purpose of output. Some examples of output devices are: Monitors, Printer, Plotters, Visual display unit (VDU), liquid crystal display (LCD), etc.


MONITOR

To display result or output from computer, a T.V like device is used which is called monitor. The monitors are also referred as C.R.T (Cathode Ray Tube), V.D.U (Visual Display Unit). The monitor assist during input from the keyboard, this display is called a soft copy. The monitor can be of various kinds, depending on the type of application. Monitors are categorized into two groups:

* Monochrome monitors

* Colour monitors


MONOCHROME MONITORS

Monochrome monitors are used specially for text editing purpose. These monitors can display only one colour. Normally amber, green or paper white.


COLOUR MONITORS

Colour monitors serves a wide range of selection according to the application. Such as red, green, blue, Enhance Graphic Array (EGA), Colour Graphic Array (CGA), Video Graphics Array (VGA), Super Video Graphics Array (SVGA).

There are two types of colour monitors:

1. CRT Monitor

2. LCD Monitor


CRT MONITOR

The CRT monitors are a lot like television set, using the same CRT or Cathorde Ray Tube technology. The CRT monitor has two major parts; the screen and the cathode ray tube (CRT). The screen is the front of the monitor and CRT is fitted inside the monitor.


LCD OR FLAT PANEL MONITOR

Another monitor type is LCD or Liquid Crystal Display. LCD monitors are a lot like CRT monitors without the bulkiness but they do not have CRT. LCD monitors use a flat lightweight surface filled with millions of tiny glass bubbles, each having a phosphoric covering. These phosphoric coverings glow to create an image. LCD screens provide clarity and flicker-free viewing.


PRINTER

A computer peripheral that puts text or a computer generated image on paper or on another medium, such as a transparency. Printer can be categorized in several ways the most common distinction is IMPACT and NON-IMPACT.


IMPACT PRINTING

Is the method used by the conventional type writers. In some type of impact printing a metal “hammer” embossed with a character strikes a print ribbon, which presses the characters image into paper. In other types the hammer strikes the paper and presses it into the ribbon characters created through impact printing can be formed by either a solid font or dot matrix printing mechanism.


NON – IMPACT PRINTING

Does not depend on the impact of metal on paper. In fact no physical contact at all occurs between the printing mechanism and the paper. The most popular non-impact methods today utilize thermal transfer, ink-jet.


TYPES OF PRINTERS
DOT MATRIX PRINTER

Any printer that produces character made up of dots using a wire pin printed head. The quality of output from a dot matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot matrix printers are often categorized by the number of pins in the printer head typically, 9 or 24.


LINE PRINTERS

Any printer that prints one line at one time, as opposed to one character at a time or one page at a time. Line printer typically produce the 11 by 17 inch “computer” printout. They are high speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single user system. Types of line printers include chain printers and band printer.

LASER PRINTERS

An electrophotographic printer that is based on the technology used by photocopiers. A focussed laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum. This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper. Finally, the electrified charge is removed from the drum and the excess toner is collected. By omitting the final step and repeating only the toner application and paper handling steps, the printer can make multiple copies.


DAISY WHEEL PRINTER

Daisy wheel printer are some times called letter quality printer because they are often used to produce attractive correspondence. The D.W.P is a flat circular device made of metal with character embossed on it. As this wheel spins at a very high speed the hammer hits the specific character against the ribbon which presses against the paper.


THERMAL TRANSFER PRINTER

It is a kind of non-impact printer. In electrothermal printing, characters are burned on to a special paper by heated rods on a print heat. They transfer ink from a wax-based ribbon onto plain paper. These printer can support high quality graphic.


INK – JET PRINTER

It is a kind of non-impact spray small dots of electrically charged ink onto a paper to form images. Ink jet printer are flexible enough to be used as plotters.


PLOTTER

Plotter is a special output device, which is used to produce high quality, perfectly proportional hard copy output. Plotters are designed to produce large drawings or images such as construction plans for buildings or blue prints for mechanical devices. Plotters have been used in automotive and aircraft design, topological surveys, architectural layouts and other similar complex drafting jobs.

A plotter is composed of a pen, a move-able carriage, a drum and a holder for chart paper. Both the pen and the paper can move up and down and back and forth. This permits very detailed drawings. Some plotter having coloured pens can make coloured drawings also.


There are two types of plotters, which are as follows:

1. Drum Plotter

2. Flatbed Plotter


DRUM PLOTTER

On the drum plotter, the pens, and the drum move concurrently in different axes to produce the image. Drum plotters are used to produce continuous output, such as plotting earthquake activity, or for long graphic output, such as structural view of a skyscraper.


FLATBED PLOTTER

On some flatbed plotters, the pen moves in both axes while the paper remains stationary. However, on most desktop plotters, both paper and pen move concurrently in much the same way as on drum plotters.


SECONDARY STORAGE DEVICES

Secondary storage devices are also called backup storage because it is used to store data. Volume of data on permanent basis which can be partially transferred to the primary storage, when required for data processing. Afterwards these devices are comparatively cheap and provide greater space to store the data /instructions are stored on secondary storage devices in the same binary codes as in primary storage.


NEEDS OF SECONDARY STORAGE DEVICE

The storage capacity of the primary storage of today’s computer is not sufficient. To store a large volume of data as a result additional memory called secondary storage is needed with most of the computer system.

These devices also provides the fast communication than I/O devices. The internal memory of a computer is a volatile memory. Therefore, we cannot save the data permanently. In that case we require secondary storage device which provide the facility to store the data for future use.


RANDOM ACCESS DEVICES

Random Access Devices are those devices on which we can directly access the data. These devices are comparatively provide the fast communication.

For example, hard disk, floppy disk, optical disk.


FLOPPY DISK

A floppy disk, also called simply a diskette or disk, is a small flexible Mylar disk coated with iron oxide on which data are stored. The floppy disk has been around since early 1970s, today it is available in three 3½ inch, 5¼ inch and 8 inch sizes. The 5¼ and 8 inch diskettes are covered by stiff protective jacket with different holes. The central big hole called hub ring which is used to hold by disk drive during rotation. The elongated read write window is used to read and write data through read/write head. The small hole next to the hub ring is called index hole which is used to locating data through computer. The cut out on the side of the floppy disk is called write protect notch. If we cover this opening with a piece of paper then we can’t write data on to disk.

In small diskette a hard plastic cover and protective metal is used to protect disk. Before using a disk we have to format a disk in which disk is divided into tracks and sectors for storing the data. Diskettes may be double sided and single sided while the storage capacity become less or more.

Floppy diskettes are more convenient to use with microcomputers. A floppy disk which is a random access device can access data fast than magnetic tape.


SEQUENTIAL ACCESS DEVICES

Sequential Access Devices are those in which we can access the data one by one in a sequence. These devices provide slow communication as compared to Random Access Device.


MAGNETIC TAPE

Magnetic tape is a sequential access device about one half or one fourth inch in size and made of Mylar (a plastic material) coated with a thin layer of iron oxide. Data can be read and write through a device which is called tape drive. The read/write head of tape drive which is an electromagnetic component read, write and erase data from magnetic tape. Magnetic tape is divided into nine separate strips or tracks in which eight tracks are used to store data and ninth track is used for error checking bit.

Magnetic tape can store large quantities of data therefore they are erasable, usable and durable secondary storage device. But it can use with large computers.


HARD DISK

Hard disk is a thin circular metal plate coated both side with a magnetic material. A hard disk pack consist of a number of disk mounted on central shaft which rotate at a speed of 2400 rpm or more. In a hard disk information is stored on both the surfaces of each disk plate except the upper and the lower surfaces of the bottom plate which are not used. Information is recorded on the track of the disk surfaces in the form of invisible tiny magnetic spot. The presence of a magnetic spot represent 1 bit and its absence represents 0 bit.

Hard disk are potentially very high capacity storage devices typically in the range of 20 megabyte to 1 gigabyte. Data are recorded on the tracks of a spinning disk surface and read from the surface by one or more read/write heads. There are two basic types of disk system.

1. Moving head

2. Fixed head


MOVING HEAD

The moving head consist of one read/write head for each disk surface mounted on an axis and which can be moved in and out. In this system each read/write head moves horizontally across the surface of the disk. So that it is able to access each track individually. Information stored on the tracks which constitute a cylindrical shape through the disk pack are therefore accessed simultaneously.


FIXED HEAD

In the fixed head system the axis are non-movable. A large number of read/write heads are distributed over the disk surfaces. One head for each track as a result no head movement is required and therefore information is accessed more quickly.


Optical Dist

An Optical disk can hold 4.7 gigabytes of data. It makes an immense amount of information available on a micro computer. Optical disks are having great impact on a storage technology these days. In optical disk technology a laser beam alters the surface of a plastic or metallic disk to represent data. To read the data a laser scans these areas and sends the data to a computer chip for conversion.

There are four kinds of optical disks available.

1. CD-ROM

2. CD-R

3. Erasable Optical Disks

4. DVD


CD-ROM

CD-ROM stands for Compact Disk Only memory. Unlike floppy disk and hard disk. Which use magnetic charge to represent 1s and 0s, optical disk use reflected light. On a CD-ROM disk 1s and 0s are represented by flat areas and bumpy areas (called pits) on its bottom surface. The CD-ROM disk is read by a laser that projects a tiny beam of light on these areas. The amount of reflected light determines whether they are represents a 1 or 0 Read-only means it cannot be written on or erased by the user.


CD-R

CD-R stands for CD Recordable. CD-R disk can be written to once. After that they can be read many times without deterioration and can't be written on or erased.


Erasable Optical Disks

Erasable Optical Disks are like CD-R except that they can be written to many times. There are two basic types of erasable optical disks. CD-RW which stands for compact disk rewriteable and MO which stands for magnetic optical.


DVD

DVD stands for digital versatile disk. DVD disks and disk drives and very similar to CD-ROM except that more data can be packed into same amount of space.DVD-ROM disks have a capacity of 4.7 gigabytes. They are being used for a variety of high-capacity needs such as recording and playing ful-length motion pictures advanced multimedia games and interactive encyclopedias.

1st Year Computer Notes CH#04 Micor Computers

Micor Computers

Introduction

Computers are the electronic devices that can follow instructions to accept input process that input and produce information. From capability point of view there are four types of computers as mentioned in the previous chapter.
1. Micro Computers
2. Mini Computers
3. Mainframe Computers
4. Super Computers

1. Micro Computers
The most widely used and fastest growing type of computer is the micro computer. There are two categories of micro computers desktop and portable. Desktop computers are small enough to fit along the side of a desk and yet are too big to carry around. Personal computer are the type of desktop. Portable computers are the micro computers that are small enough and light enough to move from one place to another. There are four categories of portable computers.
i. Laptops
ii. Notebooks
iii. Sub notebooks
iv. Personal Digital Assistants.


Components of Computer

The computer itself the hardware has many parts but each fall into one of four categories.
1. Processor
2. Memory
3. Input and Output Devices
4. Storage Devices.
Only first two categories will be discussed in this chapter, whereas next two categories will be studied in the subsequent chapter.


The CPU or Processor

The part of the computer that runs the program (executes processor) is known as the processor or central processing unit. The processor is like the brain of the computer the part that organizes and carries out the instructions that come from either user or software. The central processing unit has two components the control unit and the arithmetic logic unit.


Control Unit

The Control unit tells the rest of the computer system how to carry out a program's instruction. It directs the movement of the electronic signals between teh memory which temporarily holds data, instruction and processed information and the arithmetic logic unit. It also direct the signal between the CPU and the input and output devices.
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Arithmetic-logic Unit

The arithmetic logic unit usually called ALU performs two types of operations arithmetic and logical. The arithmetic operations are the fundamental math operations addition, substraction, multiplication and division. Logical operations consists of comparisons. i.e. two pieces of data are compared to see whether one is equal to (=), less than (<) or greater than (>) the other.


Memory (RAM)

Computer has two types of memory random access memory (RAM) and read only memory. (ROM) In this chapter only RAM will be studied whereas ROM will be studied later. RAM also known as primary memory internal memory or main memory hold.

• Data for processing

• Instruction for processing the data that is the program

• Information that is processed data waiting to be output and sent to secondary storage such as floppy disk in a disk drive.

One of the most important fact to know about memory is that part of its content is held only temporarily. In other words, it is stored only as long as computer is turned on. When the machine is turned off the contents immediately vanish.
The next important facts of know about memory is that its capacity varies in different computers.