Class 9 Computer Science Computer Software Notes

Computer Software

Computer Programs are called as Computer software, or just software. A computer Software is set of programs that guides the hardware through its job. The computer program is the non-tangible component of a computer system. A Computer software is different from computer hardware, that is the physical component of a computer system. Computer hardware and software work hand in hand cannot function without the other.

TYPES OF SOFTWARE

Computer softwares are mainly divided into two parts:
(a) System Software (b) Application Software

(A) SYSTEM SOFTWARE

System software is the software which manages and controls the hardware components and allows interaction between the hardware and the other different types of software. The computer’s operating system is a type of system software. Device drivers are also a part of this category.

System software can be separated into two different categories: Operating systems and Utility software.

OPERATING SYSTEM

A program that acts as an intermediary between a user of a computer and the computer hardware is called an operating system. The operating system is an essential component of the system software in a computer system. Application programs usually require an operating system to function.

Operating systems can be found on almost any device that contains a computer—from cellular phones and video game consoles to supercomputers and web servers. For example: UNIX, MS-DOS,WINDOWS, 98/2000/xp/7.

Functions of an operating system –

The basic functions of an operating system are:

• Booting the computer
• Performs basic computer tasks eg managing the various peripheral devices eg mouse, keyboard
• Provides a user interface, e.g. command line, graphical user interface (GUI)
• Handles system resources such as computer’s memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices
• Provides file management which refers to the way that the operating system manipulates, stores, retrieves and saves data.

• Booting the computer : The process of starting or restarting the computer is known as booting. A cold boot is when you turn on a computer that has been turned off completely. A warm boot is the process of using the operating system to restart the computer.
• Performs basic computer tasks : The operating system performs basic computer tasks, such as managing the various peripheral devices such as the mouse, keyboard and printers. For example, most operating systems now are plug and play which means a device such as a printer will automatically be detected and configured without any user intervention.
• Provides a user interface : A user interacts with software through the user interface. The two main types of user interfaces are: command line and a graphical user interface (GUI). With a command line interface, the user interacts with the operating system by typing commands to perform specific tasks. An example of a command line interface is DOS (disk operating system). With a graphical user interface, the user interacts with the operating system by using a mouse to access windows, icons, and menus. An example of a graphical user interface is Windows Vista or Windows 7.
• Handles system resources : The operating system also handles system resources such as the computer’s memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices. Programs and input methods are constantly competing for the attention of the CPU and demand memory, storage and input/output bandwidth. The operating system ensures that each application gets the necessary resources it needs in order to maximise the functionality of the overall system.
• Provides file management : The operating system also handles the organisation and tracking of files and directories (folders) saved or retrieved from a computer disk. The file management system allows the user to perform such tasks as creating files and directories, renaming files, coping and moving files, and deleting files. The operating system keeps track of where files are located on the hard drive through the type of file system. The type two main types of file system are File Allocation table (FAT) or New Technology File system (NTFS).

• File Allocation table (FAT) : It uses the file allocation table which records, which clusters are used and unused and where files are located within the clusters.
• NTFS : It is a file system introduced by Microsoft and it has a number of advantages over the previous file system, named FAT32 (File Allocation Table).NTFS also allows permissions (such as read, write, and execute) to be set for individual directories and files.

The three most common operating systems for personal computers are Microsoft Windows, Mac OS X, and Linux.

TYPES OF OPERATING SYSTEM

There are different types of operating system to support the computer system. Each type of operating system offers distinct facilities that are appropriate to the computer system in which it is used.

The operating systems are of mainly following types:

• Single-user, single task Operating System - This operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.
• Single-user, multi-tasking Operating System- This operating system mostly used by people which are using desktop and laptop computers today. Microsoft’s Windows and Apple’s MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time. For example, it’s entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.
• Multi-user Operating System : A multi-user operating system allows many different users to take advantage of the computer’s resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn’t affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.
• Real Time operating System : Real time operating system controls the environment as they have a data processing system in which the time interval required to process and respond to inputs is very small. The time taken by the system to respond to an input and display the result of the required inputted information is termed as response time.A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application’s task; the variability is jitter.A hard real-time operating system has less jitter than a soft real-time operating system. The chief design goal is not high throughput, but rather a guarantee of a soft or hard performance category. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS.
• Time-sharing operating system : Time sharing is a type of operating system that enables many people, located at various terminals, to use a particular computer system at the same time. Because of the above feature timesharing operating system is called multitasking operating system. In other words it is a logical extension of multiprogramming. Processor’s time which is shared among multiple users simultaneously is termed as time-sharing.The main purpose of Multiprogrammed batch systems, is to maximize processor use, whereas in Time-Sharing Systems the primary objective is to minimize response time.
• Distributed operating System : Distributed systems use a number of central processors to serve multiple real time application and different users. Data processing jobs are distributed among the processors accordingly to which one can perform each job most efficiently.
• Network operating System : This operating system runs on a server.This server is responsible for managing data, users, groups, security, applications, and other networking functions. The network operating system allows shared file and printer access among multiple computers in a network. This can also be referred as a local area network (LAN), or a private network. Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.
• Stand-Alone Operating System : A stand-alone operating system is a complete operating system that works on a desktop computer, notebook computer, or mobile computing device. Some stand alone operating systems are called client operating systems because they also work in conjunction with a server operating system. Client operating systems can operate with or without a network. Examples of currently used stand-alone operating systems are Microsoft Windows, Mac OS, and Linux.

• Microsoft Windows : Microsoft developed Windows operating system that has a graphical user interface. Some of the popular Windows Operating System are Windows 3.1, Windows 95, Windows 98, Windows 2000, Windows NT, Windows ME, Windows XP, Windows Vista and Windows 7. Windows 8 is the latest Windows operating systems from Microsoft. It is a graphical user interface (GUI) operating system which is very easy to learn and operate. Windows 7 provides many ways to manage the files stored on your computer. You can open, rename, print, delete, move and search for files.
• Mac OS : It is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface.
• Linux : It is a UNIX-based operating system that is available for free on the World Wide Web. Many companies, such as Red Hat, Corel and Mandrake, create easy-to-use versions of Linux that you can purchase. Red Hat Linux is a popular version that comes with the GNOME desktop environment. GNOME displays pictures on the screen to help you perform tasks. Linux is an open source code operating system. It can be copied, modified and redistributed with few restrictions. This flexibility is one of the reasons why Linux is so popular among users.

• Embedded Operating System : An embedded system is a computer that is part of a different kind of machine. Examples include computers in cars, traffic lights, digital televisions, ATMs, airplane controls, point of sale (POS) terminals, digital cameras, GPS navigation systems, elevators, digital media receivers and smart meters, among many other possibilities. In contrast to an operating system for a general-purpose computer, an embedded operating system is typically quite limited in terms of function – depending on the device in question, the system may only run a single application. However, that single application is crucial to the device’s operation, so an embedded OS must be reliable and able to run with constraints on memory, size and processing power.
• Mobile Operating System : A mobile operating system, also called a mobile OS, is an operating system that is specifically designed to run on mobile devices such as mobile phones, smartphones, PDAs, tablet computers and other handheld devices. The mobile operating system is the software platform on top of which other programs, called application programs, can run on mobile device. Examples of mobile operating systems include Apple iOS, Windows Phone, and Google Android.

• The BIOS (basic input/output system) gets the computer system started after you turn it on and manages the data flow between the operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, and printer.
• An assembler takes basic computer instructions and converts them into a pattern of bits that the computer’s processor can use to perform its basic operations.
• A device driver controls a particular type of device that is attached to your computer, such as a keyboard or a mouse. The driver program converts the more general input/output instructions of the operating system to messages that the device type can understand.
• Buffering is the pre-loading of data into a reserved area of memory (the buffer). In streaming audio or video from the Internet, buffering refers to downloading a certain amount of data before starting to play the music or movie.
• Spooling is the overlapping of low-speed operations with normal processing. Spooling originated with mainframes in order to optimise slow operations such as reading cards and printing.

GUI (Graphical User Interface)

GUI is a program interface that takes advantage of the computer’s graphics capabilities to make the program easier to use.

Basic Components of a GUI

• Pointer : A symbol that appears on the display screen and that you move to select objects and commands. Usually, the pointer appears as a small angled arrow.
• Pointing device : A device, such as a mouse or trackball, that enables you to select objects on the display screen.
• Icons : Small pictures that represent commands, files, or windows. By moving the pointer to the icon and pressing a mouse button, you can execute a command or convert the icon into a window.
• Desktop : The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop.
• Windows : You can divide the screen into different areas. In each window, you can run a different program or display a different file.
• Menus : Most graphical user interfaces let you execute commands by selecting a choice from a menu.

MS DOS (Microsoft Disk Operating System)

Short for Microsoft Disk operating system, MS-DOS is a non-graphical command line operating system derived from 86-DOS that was created for IBM compatible computers. MS-DOS originally written by Tim Paterson and introduced by Microsoft in August 1981 and was last updated in 1994 when MS-DOS 6.22 was released. MS-DOS allows the user to navigate, open, and otherwise manipulate files on their computer from a command line instead of a GUI like Window.

DOS has a character user interface (CUI) i.e : Communication between a computer and the user can be done by using characters. In Dos, one has to key in the commands on the prompt. Prompt is a place where commands are issued. It may look like C:\> or C:\windows\>

MS DOS Commands

• ansi.sys: Defines functions that change display graphics, control cursor movement, and reassign keys. (Type: File)
• append: Causes MS-DOS to look in other directories when editing a file or running a command. (Type: External)
• assign: Assign a drive letter to an alternate letter. (Type: External)
• assoc: View the file associations. (Type: Internal)
• attrib: Display and change file attributes. (Type: External)
• call: Calls a batch file from another batch file. (Type: Internal)
• cd: Changes directories. (Type: Internal)
• chcp: Supplement the International keyboard and character set information. (Type: External)
• chdir: Changes directories. (Type: Internal)
• cls: Clears the screen. (Type: Internal)
• cmd: Opens the command interpreter. (Type: Internal)
• color: Change the foreground and background color of the MS-DOS window. (Type: Internal)
• comp: Compares files. (Type: External)
• convert: Convert FAT to NTFS. (Type: External)
• date: View or change the systems date. (Type: Internal)
• debug: Debug utility to create assembly programs to modify hardware settings. (Type: External)
• delete: Recovery console command that deletes a file. (Type: Internal)
• dir: List the contents of one or more directory. (Type: Internal)
• disable: Recovery console command that disables Windows system services or drivers. (Type: Recovery)
• diskcomp: Compare a disk with another disk. (Type: External)
• diskcopy: Copy the contents of one disk and place them on another disk. (Type: External)
• echo: Displays messages and enables and disables echo. (Type: Internal)
• edit: View and edit files. (Type: External)
• erase: Erase files from computer. (Type: Internal)
• exit: Exit from the command interpreter. (Type: Internal)
• expand: Expand a Microsoft Windows file back to it’s original format. (Type: External)
• extract: Extract files from the Microsoft Windows cabinets. (Type: External)
• find: Search for text within a file. (Type: External)
• format: Command to erase and prepare a disk drive. (Type: External)
• ftp: Command to connect and operate on an FTP server. (Type: External)
• fType: Displays or modifies file types used in file extension associations. (Type: Recovery)
• goto: Moves a batch file to a specific label or location. (Type: Internal)
• help: Display a listing of commands and brief explanation. (Type: External)
• if: Allows for batch files to perform conditional processing. (Type: Internal)
• ipconfig: Network command to view network adapter settings and assigned values. (Type: External)
• keyb: Change layout of keyboard. (Type: External)
• label: Change the label of a disk drive. (Type: External)
• lock: Lock the hard drive. (Type: Internal)
• logoff: Logoff the currently profile using the computer. (Type: External)
• logon: Recovery console command to list installations and enable administrator login. (Type: Recovery)
• map: Displays the device name of a drive. (Type: Recovery)
• mem: Display memory on system. (Type: External)
• mkdir: Command to create a new directory. (Type: Internal)
• move: Move one or more files from one directory to another directory. (Type: Internal)
• ping: Test and send information to another network computer or network device. (Type: External)
• power: Conserve power with computer portables. (Type: External)
• print: Prints data to a printer port. (Type: External)
• rd: Removes an empty directory. (Type: Internal)
• rename: Renames a file or directory. (Type: Internal)
• rmdir: Removes an empty directory. (Type: Internal)
• share: Installs support for file sharing and locking capabilities. (Type: External)
• shift: Changes the position of replaceable parameters in a batch program. (Type: Internal)
• shutdown: Shutdown the computer from the MS-DOS prompt. (Type: External)
• set: Change one variable or string to another. (Type: Internal)
• start: Start a separate window in Windows from the MS-DOS prompt. (Type: Internal)
• sys: Transfer system files to disk drive. (Type: External)
• telnet: Telnet to another computer or device from the prompt. (Type: External)
• time: View or modify the system time. (Type: Internal)
• Type: Display the contents of a file. (Type: Internal)
• undelete: Undelete a file that has been deleted. (Type: External)
• unformat: Unformat a hard drive. (Type: External)
• unlock: Unlock a disk drive. (Type: Internal)
• ver: Display the version information. (Type: Internal)
• xcopy: Copy multiple files, directories, or drives from one location to another. (Type: External)

Utility Software

Utility software is software that helps to maintain and protect the computer system. It does not directly interface with the hardware. Examples include anti-virus software, firewalls, disk defragmenters and so on . System utilities are the core software functions that allow you to manage your computer in ways that you would find it inconceivable to be without.

Functions of System Utility:

• Disk Cleanup : Disk Cleanup is a function that comes with all versions of Windows Operating Systems. Disk Cleanup allows for you to scan your entire hard drive to search for extra room by deleting any unneccessary files such as temporary files from the Internet and cookies that are downloaded when you visit webpages.
• IDisk Defragmentation : Defragmentation is the process of locating the noncontiguous fragments of data into which a computer file may be divided as it is stored on a hard disk, and rearranging the fragments and restoring them into fewer fragments or into the whole file.
• System Restore : System Restore is a Windows utility that allows a user to restore their computer data to a specific former state (known as a restore point), undoing changes made since that time.
• Disk Compression : Disk compression is a type of function that allows for a program to search your hard drive and compress files, particularly old or unused files. It also serves to free up space, which is the main function of disk compression software.
• Antivirus : It is used to scan computer for viruses and prevent the computer system files from being corrupt.

(b) APPLICATION SOFTWARE

(Also known as ‘apps’) are designed to achieve a complete task or a set of tasks. Application software consists of the programs for performing varied tasks particular to the machine’s utilization. There are various examples of application software that include MS Word, MS Excel, a console game, database systems, desktop publishing systems, program development software, a library management system etc.

• Retail software: This type is sold off the shelves of retail stores. It involves expensive packaging that are designed to appeal customers .These are high on cost .
• OEM software: OEM stands for “Original Equipment Manufacturer” and refers to that sold in bulk to resellers, designed to be bundled with hardware.
• Shareware : It is a software that can be downloaded from the Internet. There is a license period in which the user is allowed to try the program for free .After the stipulated period (in the license usually thirty days), it must be purchased or uninstalled.
• Adware: This software has advertisements built into the program itself.It is a free software.These softwares use a live Internet feed and constant bandwidth to upload new advertisements.
• Spyware: Spyware is normally free. These can be shareware. For example, a multimedia player might profile what music and video the user wants to play.
• Freeware: Freeware is also downloadable off the Internet and is free of charge.Freeware is only free for personal use. A paid license is required for commercial use. Freeware does not contain spyware or adware.

There are various types of application software :

I. Word Processing : The most important computer application is that they are most commonly used to create, edit, and print documents. E.g. Microsoft Word, Google Docs, AppleWorks, Openoffice.org etc.

II. Spreadsheet : A spreadsheet is a type of document that stores the entire data in a grid form consisting of horizontal rows and vertical columns. E.g. Microsoft Excel, Correl Quattro Pro etc

III. Presentation Graphics : Presentation Graphics also called as the presentation software is a type of application program that helps you to create different timing and organized sequence of information and pictures. E.g.Microsoft PowerPoint, Apple Keynote, OpenOffice Impress etc.

IV. Multimedia authoring : Multimedia authoring software helps you to create a a presentation that has a variety of feature such as the audio and video sequences.

V. Database software : Database software allows you to create and manage a database. A database is a collection of data organized to allow access, retrieval, and use of that data. E.g.Microsoft Access, Corel Paradox, Lotus Approach etc.

VI. Desktop publishing(DTP): Desktop publishing(DTP) software is used to design and produce sophisticated documents. DTP is developed specifically to support page layout. E.g.Adobe InDesign,Adobe PageMaker,Corel Ventura,Coreldraw,Microsoft Office Publisher etc.

A videoconference is a meeting between two or more geographically separated people who use a network or the Internet to transmit audio and video data.

PROGRAMMING LANGUAGES

A programming language is a set of commands, instructions, and other syntax use to create a software program. Languages that programmers use to write code are called “high-level languages.” This code can be compiled into a “low-level language,” which is recognized directly by the computer hardware.

• Low Level Languages: Low level computer languages are machine codes or close to it. Computer cannot understand instructions given in high level languages or in English. It can only understand and execute instructions given in the form of machine language i.e. language of 0 and 1.
  • IMachine Language : The set of instructions executed directly by a computer’s central processing unit (CPU) is called Machine code .In machine language each and every instruction performs specific operation.
  • Assembly Language : A personal computer has a microprocessor of its own that manages the computer’s arithmetical, logical and control activities. Low-level assembly language is designed for representation of all the instructions in a symbolic code yet in a more understandable form for a specific family of processors.
• High-Level Language : Writing programs was made easier with time. High-level programming languages allowed the specification of writing a program closer to those used by human beings. Fortran II was one of the first high level language introduced in about 1958.

• Assembler : It is used to convert the assembly language into machine language (i.e. 0 or 1). This language consists of mnemonic codes which are difficult to lean and is machine dependent.
• Compiler : Compiler is a special program which reads a program in source language and translates into an equivalent other language. Also it reports the errors in the source program to its user, if there are any.
• Interpreter : A high-level programming language translator that translates and runs the program at the same time. It converts one program statement into machine language, executes it, and then proceeds to the next statement.
• Loader : In loading, a routine of a program is not loaded until it is called by the program. All routines are kept on disk in a re-locatable load format. The main program is loaded into memory and is executed.
• Linker : Linking as the name suggests is the process of combining various pieces of code and data together to form a single executable that can be loaded in memory.
• Debugging : In computers, debugging is the process of locating and fixing or bypassing bugs (errors) in computer program code or the engineering of a hardware device.

4GL and 5 GL

• 1GL or first-generation language was (and still is) the machine language generation.It refers to the level of instructions and data that is fed to the processor of a computer. (which in conventional computers is a string of 0s and 1s).
• 2GL or second-generation language is the assembly language generation. An assembler converts the assembler language statements into machine language.
• 3GL or third-generation language is a “high-level” programming language, such as C /C ++or Java.
• 4GL or fourth generation (programming) language is a grouping of programming languages that attempt to get closer than 3GLs to human language, form of thinking and conceptualisation.
• 5GL or fifth-generation language is a programming language that has a visual or graphical development interface to develop the source code but compiled with a 3GL or 4GL language compiler.

NUMBER SYSTEM

In general, in any number system there is an ordered set of symbols known as digits with rules defined for performing arithmetic operations like addition, subtraction, multiplication and division. A collection of these digits makes a number which in general has two parts-integer and fractional.

• Binary: Base 2, Symbols 0,1. Example: 1011.11
• Octal: Base 8, Symbols 0,1,2,3,4,5,6,7. Example: 3567.25
• Decimal: Base 10, Symbols 0,1,2,3,4,5,6,7,8,9. Example: 3974.57
• Hexadecimal: Base 16, Symbols 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F. Example: 3FA9.56

Number Conversions

Question. Find the decimal equivalent of binary number 11111.
Answer: The equivalent decimal number is,
\( = 1 \times 2^4 + 1 \times 2^3 + 1 \times 2^2 + 1 \times 2^1 + 1 \times 2^0 \)
\( = 16 + 8 + 4 + 2 + 1 = ( 31 )_{10} \)

Question. Express the 25.5 decimal number in the binary form.
Answer: Integer Part: (25)10 = (11001)2
Fraction part:
\( 0.5 \times 2 = 1.0 \)
i.e., \( 0.5_{10} = 0.1_2 \)
Therefore \( 25.5_{10} = 11001.1_2 \)

Question. Convert conversion (444.499)10 into Octal.
Answer: Division of 444 by 8 gives remainders 4, 7, 6 (from bottom to top). Fractional conversion: \( 0.499 \times 8 = 3.992 \) (3), \( 0.992 \times 8 = 7.936 \) (7), \( 0.936 \times 8 = 7.488 \) (7), \( 0.488 \times 8 = 3.904 \) (3).
Thus, octal equivalent is \( (444.499)_{10} = (674.3773)_8 \)

Question. To convert (377)8 into binary, replace each significant digit by its 3-bit binary equivalent.
Answer: (377)8 = 3 7 7
= 011 111 111
Thus, (377)8 = (011111111)2

Question. To convert (1D5)16 into binary, replace each significant digit by its 4-bit binary equivalent.
Answer: (1D5)16 = 1 D 5
= 0001 1101 0101
Thus, (1D5)16 = (000111010101)2

Some important terms in computer software –

• Kernel: The nucleus of an operating system. It is the closest part to the machine level and may activate the hardware directly or interface to another software layer that drives the hardware.
• Shell: The outer layer of a program that provides the user interface, or way of commanding the computer.
• Fork: fork() creates a new process by duplicating the calling process. The new process, referred to as the child, is an exact duplicate of the calling process, referred to as the parent.
• Thread: thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler.
• Deadlock: A condition that occurs when two processes are each waiting for the other to complete before proceeding.
• Multiprocessing: Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system.