Chapter 4 – Computer Software

A computer Network is 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.h.

Types of Software

Computer softwares are mainly divided into two parts:

  1. System Software
  2. Application Software

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:

  1. Operating systems
  2. Utility software

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:

I.  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.

II. 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.

III. 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.

IV. 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.

V. 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.

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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 Mac OS 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 time sharing operating system is called multitasking operating system. In other words it is a logical extension of multi programming. Processor’s time which is shared among multiple users simultaneously is termed as time-sharing. The main purpose of Multi programmed 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 Net Ware, and BSD.


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.

  1. 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.
  2. 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.
  3. 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.


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.

Thousands of connected embedded devices have been built on Windows Embedded platforms, from portable ultrasound machines to GPS devices and from ATMs to devices that power large construction machinery. With comprehensive features, easy-to-use and familiar Microsoft development tools, free evaluation kits and access to a large network of community support, working with Windows Embedded Products helps yield faster time to market for your devices and decreased development costs.


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.

Operating systems for mobile devices generally aren’t as fully featured as those made for desktop or laptop computers, and they aren’t able to run all of the same software. However,you can still do a lot of things with them, like watch movies, browse the Web, manage your calendar, and play games.

  • 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. Having an advance supply of audio samples or video frames in memory at all times prevents disruption if there are momentary delays in transmission while the material is being played. Even a live broadcast would have a few seconds of delay built in.
  • 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. Card input was read onto disk and printer output was stored on disk. In that way, the business data processing was performed at high speed, receiving input from disk and sending output to disk. Subsequently, spooling is used to buffer data for the printer as well as remote batch terminals.

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 

Graphical user interfaces, such as Microsoft Windows and the one used by the Apple Macintosh, feature the following basic components:

  • 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. Text -processing applications, however, use an I-beam pointer that is shaped like a capital I.
  • 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. You can also move the icons around the display screen as if they were real objects on your desk.
  • 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. You can move windows around the display screen, and change their shape and size at will.
  • 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>

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

I. 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 unnecessary files such as temporary files from the Internet and cookies that are downloaded when you visit webpages. You can find Disk Cleanup in Windows XP by going to the Start menu → All Programs → Accessories →System Tools → Disk Cleanup.

II. Disk 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.

III. 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. System Restore can be found by going to Start → All Programs → Accessories → System Tools → System Restore

IV. 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.

V.  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.

Table shows difference between System software and Application software :

System Software Application Software
Enable the computer to function Usage Enable user to work efficiently with documentation
Compulsory Need Optical depends on usage and needs
Each computer need one system system software Number Software Each computer can have more than one application
Independent can use without application software Dependency Depende – application software cannot work without Application software
Provide environment in which the application run Function Provides the environment to enable user to accomplish specific task

  • 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. In such a case the software files the program whene verit is called upon 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. If it is found to contain either of these, it is reclassified as such.

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.  Word processing software allows users to create and manipulate documents that contain text and graphics. With word processing software, you can insert clip art into a document; change margins; find and replace text; use a spelling checker to check spelling; place a header and footer at the top and the bottom of a page; and vary font (character design), font size (character scale), and font style (character appearance).

E.g. Microsoft Word, Google Docs, Apple Works, Open 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. This row/column structure  allows the analysis of data using formulas and calculations. With spreadsheet software, data is organized in rows and columns, which collectively are called a worksheet. The intersection of a row and column, called a cell, can contain a label (name of cells), a value (number), or a formula or function that performs calculations on the data and displays the result.

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 that present a story or help in giving a  public presentation of information through a slide show.

 E.g. Microsoft  PowerPoint,  Apple Keynote,  Open Office Impress,  Corel Presentations,  Adobe Persuasion 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. Business presentation software usually enables you to include images and sometimes audio and video developed with other tools.

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. A query is used to retrieve data according to specified criteria, which are restrictions the data must meet.

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, which is the process of arranging text and graphics in a document. Complete DTP involves combination of type setting, graphic design, page layout and printing the document.

E.g. Adobe In Design, Adobe Page Maker, Corel Ventura, Corel draw, Microsoft Office Publisher etc.

A video conference 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.

(a) 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. There are two types of low level languages:

I.  Machine 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. The machine code is in the form a numerical  code (i.e. not assembly code) and is  the lowest-level representation of a compiled and/or assembled computer program. Machine language is also called as a primitive and hardware-dependent programming language. Writing programs directly in numerical machine code is tedious task.

II.  Assembly Language : A personal computer has a microprocessor of its own that manages the computer’s arithmetical, logical and control activities. All these operations are managed through a set of instructions by each family of processors. These operations are  handled by getting input from keyboard and displaying information on screen and performing various other jobs. These set of instructions are called machine language instructions.

Machine language instructions are in the form of strings of 1’s and 0’s. Machine language is quite obscure and complex for using in software development. For this very reason 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.

(b) High-Level Language : Writing programs was made easier with time. Earlier languages that were developed, during the development of computers required knowledge of the internal workings of the computer, hence attempts were made to ease the programming where the knowledge on the the internal workings of the computer was not required. High-level programming languages allowed the specification of writing a  program closer to those used by human beings. With the advent of high level languages, programming became far easier, less error-prone and also removed the programmer from having to know the details of the internal structure of a particular computer. 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.

Types of Error

Errors are either syntactic or semantic:

Syntax errors are errors in the program text.

Semantic errors are mistakes concerning the meaning of a program construct.

  • 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. This differs from regular executable programs that are presented to the computer as binary-coded instructions. Interpreted programs remain in the source language the programmer wrote in, which is human readable text.
  • 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. Other routines methods or modules are loaded on request. Dynamic loading makes better memory space utilization and unused routines are never loaded.
  • 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. Linking can be done at compile time, load time (by loaders) and  at run time (by application programs) too.
  • 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
Language Application Area Developer
COBOL(Common Business Oriented Business Oriented Language) Business applications Grace Hopper in 1959
FORTRAN (Formala Translation) Engineering & Scientific Applications IBM in 1957
PASCAL General use and as a teaching tool Niklaus wirth in 1972
C & C++ General Purpose – currently most popular C/C++ Bjarne Stroustrup in 1983. Dennis Ritchie in 1972
LISP (List Processing) Artificial Intelligence John Mc carthy in 1958
JAVA General Purpose – Internet Oriented Programming James gosling in 1995

4GL and 5 GL

4GL and 5GL represent the leaps or the “generations” in the evolution of programming languages.

  • 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.
  • A 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. 4th generation language, is known as the  domain specific language, or a high productivity language.
  • 4GLs are the  programmer-friendly generation of programming. They are easier to write  and hence improve the programming efficiency by using words and phrases close to the English language, with appropriate, use of icons, graphical interfaces and symbolical representations. 4GLs have also increased the number of professionals to be able to develop skills set in software development.
  • 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. There are several business corporations that make these languages such as the Microsoft, Borland, IBM, etc.
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.

The digits in a number are placed side by side and each position in the number is assigned a weight or index.

Table below gives the details of commonly used number systems.

Number System Base or radix (b) Symbol used(di or d–f) Weight assigned to position example
Binary 2 0,1 2–i 2–f 1011.11
Octal 8 0,1,2,3,4 8–i 8–f 3567.25
Decimal 10 0,1,2,3,4,5 10–i 10–f 3974.57
Hexadecimal 16 0,1,2,3,4,5,6,7,8 , A,B,C,D,E,F 16–i 16–f 3FA9.56

1. Binary Number System 

The number system with base (or radix ) two is known as the binary number system. Only two symbols are used to represent numbers in this system and these are 0 and 1, these are known as bits. It is also known as base 2 system. It is a positional system, that is every position is assigned a specific weight left – most bit is known as Most Significant Bit (MSB) and the right – most bit is known as the Least Significant Bit (LSB). Any number of OS can be added to the left of the number without changing the value of the number. A group of four bits is known as nibble and a group of eight bits is known as a byte. Table shows binary numbers and their equivalent decimal numbers.

Table : 4-bit binary numbers and their corresponding decimal numbers.

Binary Number Hexa decimal Decimal Number
B3 B2 B1 B0 H D1 D0
0 0 0 0 0 0 0
0 0 0 1 1 0 1
0 0 1 0 2 0 2
0 0 1 1 3 0 3
0 1 0 0 4 0 4
0 1 0 1 5 0 5
0 1 1 0 6 0 6
0 1 1 1 7 0 7
1 0 0 0 8 0 8
1 0 0 1 9 0 9
1 0 1 0 A 1 0
1 0 1 1 B 1 1
1 1 0 0 C 1 2
1 1 0 1 D 1 3
1 1 1 0 E 1 4
1 1 1 1 F 1 5

2. Decimal Number System
It consists of ten digits from 0 to 9. These digits can be used to represent any numeric value. It is also known as base 10 System.

3. Octal Number System
It is one of the popular number system. It consists of 8 digits from 0 to 7. It is also known as base 8 system.

4. Hexadecimal Number System
hexadecimal means 16. These are 16 combinations of 4-bit binary numbers and sets of 4-bit binary number can be entered in the microprocessor in the form of hexadecimal digits.

Since 16 digits are used, the heights are in powers of 16. The decimal equivalent of a hexadecimal string equals sum of all hexadecimal digits multiplied by their Weights.

e.g., (F 8 E . 2 B)16 = F × 162 + 8 × 161 + E × 160 + 2 × 16-1 + B × 16-2

= 15 × 162 + 8 × 161 + 14 × 16 + 2 × 16-1 + 11 × 16-2

= 3840 + 128 + 14 + 2⁄16 + 11⁄256 = (3982.16796875)10.

Number Conversions

Binary-Decimal Conversion

Any binary number can be converted into its equivalent decimal number using the weights assigned to each bit position. Since only two digits are used, the weights are powers of 2. These weights are 20 (Units), 21(twos), 22(fours) , 23(eights) and 24(sixteen). If longer binary number involved, the weights continue in ascending powers of 2.

The decimal equivalent of a binary number equals the sum of all binary number equal the sum of all binary digits multiplied by their weights.

Example : Find the decimal equivalent of binary number 11111.

Solution : The equivalent decimal number is,

= 1 × 24 + 1 × 23 + 1 × 22 + 1 × 21 + 1 × 20

= 16 + 8 + 4 + 2 + 1 = (31)10

Decimal-to Binary Conversion

Any decimal number can be converted into its equivalent binary number. For integers,the conversion is obtained by continuous division by 2 and keeping track of the remainders, while for fractional parts, the conversion is effected by continuous multiplications by 2 and keeping track of the integers generated.

Example : Express the 25.5 decimal number in the binary form.

Solution: Integer Part
Thus,(25)10 = (11001)10


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Octal-Binary Conversion
It can be explained through the following example : To convert (377)8 into binary, replace each significant digit by its 3-bit binary equivalent.

(377)8 = 3       7       7

=  011  111  111

Thus, (377)8 = (011111111)2
Binary – Hexadecimal Conversion
e.g., (10100110111110)2 = (0010  1001  1011  1110)2 = (2  9  B  E)16 × 1

Hexadecimal -Binary Conversion

It can be  explained through an example. To  convert (1D5)16  into binary,  replace each significant digit by its 4-bit binary equivalent.

(1D5)16 = 1       D       5

= 0001  1101  0101

Thus, (1D5)16 = (000111010101)2


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. The kernel orchestrates the entire operation of the computer by slicing time for each system function and each application as well as managing all the computer’s resources. It typically resides in memory at all times.

Shell : The outer layer of a program that provides the user interface, or way of commanding the computer. The term originally referred to the software that processed the commands typed into the Unix operating system . For example, the Bourne shell was the original command line processor, and C shell and Korn shell were developed later. In DOS, the default shell was COMMAND.COM

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, except for the following points. The child has its own unique process ID, and this PID does not match the ID of any existing process group. The child’s parent process ID is the same as the parent’s process ID.

Thread : thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler (typically as part of an operating system). The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is a component of a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.

Deadlock : A condition that occurs when two processes are each waiting for the other to complete before proceeding. The result is that both processes hang. Dead locks occur most commonly in multitasking and client/server environments. Ideally, the programs that are deadlocked, or the operating system, should resolve the deadlock, but this doesn’t always happen.

Multiprocessing : Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them.