Operating system

UNIT-6 Operating System

6.1  Fundamental concept 6.1.1  Introduction to Operating System 6.1.2  Role of Operating System 6.1.3  Functions of an Operating System 6.1.4  Types of Operating System: Based on Processing Method(Batch, Multitasking, Multiprocessing, Timesharing, Real Time), Based on User Interface(GUI, CUI), Based on Mode of User( Single-user & Multi-user) 6.2 Disk Operating System(DOS) 6.2.1  Introduction to CUI and it’s feature 6.2.2  Introduction to DOS 6.2.3  Common DOS Commands(External and Internal Commands) 6.2.4  Concept of File and Directory 6.2.5  Wildcards and Pathname 6.2.6  System Files : Config.sys, IO.sys, MSDOS.sys, autoexec.bat 6.3  Windows operating system 6.3.1  Introduction to GUI and its features 6.3.2  Working with a Window Environment 6.3.3  Working with a Windows Application Program 6.3.4  Working with Files and Folders 6.3.5  Customizing the Taskbar and Desktop 6.3.6  Customizing Windows 6.3.7  Use of Accessories 6.4 Concept of Open sources operating system 6.4.1 Introduction to Open Sources Operating System 6.4.2 Introduction to Linux, UNIX

Introduction to Operating System

An operating system is an organized collection of  programs that controls and manages the overall resources (memory, storage, processor, i/o devices etc) and operations of the computer system. It also acts as an interface between machine and user. Simply, it is a software program that enables the computer hardware to communicate and operate with the computer software. For examples: Windows, Windows Vista, UNIX, LINUX, DOS and OS/2. etc

The organization or architecture of operating systems deal with the internal structure of OS, mainly it is divided into 3 layers as shown in figure below:

OS Kernel

A main part of OS always remains in main memory during the running of a computer is called OS kernel. It controls all running programs and the hardware resources. It is directly communicate with hardware.

Utility software

Utility software helps to manage, maintain and control computer resources. It is to make system up-to-date and efficient. For example: scandisk, disk-cleanup, disk defragmenter, device drivers, file compression, backup-recovery, antivirus, web-browser etc.

OS application

Application software is a program or group of programs designed for end users. It is developed in order to fulfill the user requirements. Basic application software also provides by the OS such as Notepad, WordPad, Paint, and simple games etc.

Hardware

Hardware is physical part of computer such as CPU, Main memory, I/O Devices, etc.

Roles/Purposes of Operating System

• Easy interaction between human and computer( hardware)
• Starting computer operation automatically.
• Loading and scheduling users’ programs/processes.
• Controlling I/O devices
• It provides the tasks to different peripheral devices.
• Managing various types of memories such as primary, secondary, cache etc.
• Providing security to users’ jobs and files.
• Accounting hardware resources and handling network communication.
• Allowing users to share data and software among themselves.
• Preventing the system from unauthorized user, programs, hackers, crackers, viruses etc.

Function of Operating system

·         Input & Output management.

·         Command interpreter

·         Process management.

·         Memory management.

·         File management.

·         Security management.

·         User interface.

·         Job management.

·         Data management.

·         Controlling resources.

·         Interrupt handling

·         Deadlock prevention.

·         Virtual storage management.

Explained as below:

 ·         Job Management: OS manages the job waiting to be processed. It recognizes the jobs, identifies their priorities, allocates the memory for the job, schedules and finally runs each job at the appropriate moment.

·         Data Management: Data management keeps track of the data on disk, tape and optical storage devices. The operating system's file system knows where that data are physically stored.

·         Virtual Storage Management: OS is used for virtual memory management. OS makes possible to increase the capacity of main memory without actually increasing its size.

·         Input/output Management: An OS keeps track of I/O devices i.e. which device is in use and by which job that device is using. It decides which job should use which device and how long. It allocates the devices to the job and deallocates device after completion of the job.

·         Process Management: The main activities of process management are job queuing, job scheduling, keeping track of the status of each process etc.

·         Protection and Security: OS job is to secure data inside the memory of computer. Operating systems provide password protection to keep unauthorized users out of the system.

·         User Interface: An interface is a set of commands or menus through which a user communicates with a program. OS acts as an interface between a user of a computer and the computer hardware.

·         Command interpreter: It takes command from the user and then OS translate it into a detail meaningful instruction, which can understand easily. It is to get and execute the user specified command.

·         Memory management: its function of an operating system takes care of allocation and de-allocation of memory space to the programs in need of these resources.

·         File management: its functions of an OS takes care of file related activities such as organization, storage, retrieve, naming, sharing and protection of files.

·         Interrupt handler: An interrupt is a signal to the kernel (i.e., the core of the operating system) that an event has occurred, and this results in changes in the sequence of instructions that is executed by the CPU (central processing unit). In other word, an interrupt is a signal from a device attached to a computer or from a program within the computer that causes the main program that operates the computer (the operating system) to stop and figure out what to do next. There are two types of interrupt as:

·         Hardware interrupt (external): - It is a signal to the system from an event that has originated in hardware (I/O devices), such as the pressing of a key on the keyboard, a movement of the mouse or a progression in the system clock. External interrupt can also divided into two types:

Maskable interrupt: It is lower priority interrupt than non-Maskable interrupt

Non-Maskable interrupt:  It has higher priority than the Maskable interrupt.

·         Software interrupt (internal):  It is generated or caused by programs or software. It arises from illegal or erroneous use of an instruction or data. It is also called traps. Example: from ROM BIOS, registered overflow, attempt to divide by zero, stack overflow and invalid operation code.

·         Virtual memory management:  Virtual memory is the part of the hard disk which act/reserved as RAM. When a RAM module becomes full, the CPU accesses the hard disk to store and retrieve data as RAM.

Paging:

           In paging system, each process is divided into a number of fixed length blocks called 'pages', typically 4K bytes in length. Memory space is viewed as a series of 'page-frames' of the same size. When a process is to be executed, only the pages that are immediately required are loaded into memory.

Swapping:

               In a virtual memory system, Swapping is a memory management technique in which high priority process is swap in main memory and low priority process from main memory is swap out. When high priority process is completed, low priority process is swap in again. 

Technical term:

Buffering

             A buffer is a region of memory used to temporarily hold data while it is being moved from one place to another. Typically, the data is stored in a buffer as it is retrieved from an input device(such as a keyboard) or just before it is sent to an output device (such as a printer). However, a buffer may be used when moving data between processes within a computer. So, buffering is a process of placing the data in a buffer in order to increase the processing capability of a device.

Spooling (Simultaneous Peripheral Operations On-Line)

              In computer science, spooling refers to a process of transferring data by placing it in a temporary working area where another program may access it for processing at a later point in time. The term 'spool' is an acronym of 'Simultaneous Peripheral Operations On-Line'. This temporary working area could be a file or storage device, but probably not a buffer.

           For example: By using a process spooling, multiple users can send jobs to a printer simultaneously. When users send documents (known as print jobs) to a networked printer, each job is stored temporarily on the file server. As the printer finishes printing the current job, the file server sends the next job to the printer so that it can be printed).

Types of Operating System

Based on Processing Method

a)      Batch processing OS

b)      Multiprogramming OS

c)      Multitasking OS

d)     Multiprocessing OS

e)      Time sharing Management

f)       Real-time system

g)      Network and Distributed system

h)      On-line Processing

Based on User Interface

a)      Graphical User Interface(GUI)

b)      Character User Interface(CUI)

Based on Mode of User

a)      Single User OS

b)      Multi user OS

Based on Processing Method

Batch processing OS

 Batch processing is a technique in which Operating System collects one programs and data together in a batch before processing starts. Operating system does the following activities related to batch processing.

·         OS defines a job which has predefined sequence of commands, programs and data as a single unit.

·         OS keeps a number a jobs in memory and executes them without any manual information.

·         Jobs are processed in the order of submission i.e first come first served fashion.

·         When job completes its execution, its memory is released and the output for the job gets copied into an output spool for later printing or processing.

 EXAMPLE --: batch operating system is following.
1-DOS (Disk operating system. 2- IBM OS/2.
3- Windows 95, 98 and ME.
Note-  A batch is group of similar types of jobs (combination of data and program).

Advantages/ Benefits

·         It allows sharing of computer resources among many users and programs

·         It shifts the time of job processing.

·         It avoids idling the computing resources with minute by minute.

Disadvantages

·         Lack of interaction between the user and job.

·         CPU is often idle, because the speed of the mechanical I/O devices is slower than CPU.

·         Difficult to provide the desired priority.

·         The time taken between job submission and completion is very high.

Multi-programming Operating system

             A multi-programming operating system is one that allows end-users to run more than one program in a main memory of the computer at a time. Multiprogramming assumes a single shared processor. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. E.g. Windows XP, Linux etc.

Advantages

·         High and efficient CPU utilization.

·         User feels that many programs are allotted CPU almost simultaneously.

Disadvantages

·         CPU scheduling is required.

·         To accommodate many jobs in memory, memory management is required.

Multitasking operating system

                 Multitasking is a logical extension of multi-programming system that supports multiple programs to run concurrently. In multitasking more than one task are executed at the same time. E.g. windows, Mac OS, UNIX, Linux etc

There are two basic types of multitasking:

·         Pre-emptive: -In pre-emptive multitasking, the OS allows CPU time slices to each program. E.g. OS/2, Windows 95, Windows NT and UNIX etc.

·         Non-pre-emptive: -In non-pre-emptive multitasking, each program can control the CPU for as long as it needs.

Multiprocessing OS (parallel processing)

                  Multiprocessing operating system is the one which runs on the computer having more than one processor and all these processors share some or all of the same memory. Such OS simultaneously executes two or more jobs at a single time. E.g. UNIX, MVS (Multiple Virtual System/ Storage) etc.

Time sharing

            In time-sharing systems, the CPU executes multiple jobs by switching among them, but the switches occur so frequently that the users can interact with each program while it is running. In other word, allows two or more users to run programs at the same time. E.g. BSD UNIX, TOPS-10 (DEC), TOPS-20 (DEC), Tenex etc.

Advantages

·         Provide advantage of quick response.

·         Avoids duplication of software.

·         Reduces CPU idle time.

Disadvantages

·         Problem of reliability.

·         Question of security and integrity of user programs and data.

·         Problem of data communication.

Real-time system

Real time Operating system is method which controls environment by receiving data, processing them and taking action quickly at that time. Real-time operating systems are used to control machinery, scientific instruments and industrial systems. Examples:  Lynx, MTOS, QNX, RTMX, RTX, and VxWorks etc

There are two types:

·         Soft real time operating system: - In Soft Real Time System, tasks are completed as fast as possible without having to be completed within a specified timeframe.

·         Hard real time operating system: - In Hard Real Time System however, not only must tasks be completed within a specified timeframe, but they must also be completed correctly.

Applications

§  Rocket launching system.

§  Monitoring and controlling nuclear power station.

§  Robotics

§  Traffic light control

Network and Distributed system

Network operating system is used when numbers of computers are connected in a network. It works under client/ server principle. The server provides services such as mail, database, printing etc and client computer take services provided by server. Examples of network operating systems are Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.

A distributed operating system manages a group of independent computers and makes them appear to be a single computer. Example: IRIX, DYNIX,

AIX, Solaris, Mach/OS and OSF/1 etc

On-line Processing

Online processing is an automated way to enter and process data or reports continuously as use as the source documents are available. Eg Windows, Mac etc

Based on the user interface method

Interface is a common boundary between the user and the computer system. It allows user to communicate with the computer. So, it makes interaction of user with the system. Generally, there are two main types of user interfaces:

a)      CUI (Character User Interface)/CLI (Command Line Interface)/TBI (Text Based Interface)

CUI means you have to take help of a keyboard to type commands to interact with the computer. In the CUI, the user providers the input by typing a command string with the computer keyboard and the system provide output by printing text on the computer monitor as in MS DOS or command prompt.  So, the commands are accepted and executed by a part of the OS called CUI. Examples: MS-DOS, PC-DOS, UNIX, LINUX, VMS etc.

Features of CUI

·         CUI is more textual and less user-friendly.

·         CUI based OS are usually 8 or 16 bits operating system.

·         Difficult to use and learn.

·         It needs less amount of memory space.

·         It is faster than GUI.

·         It does not often support pointing devices like as mouse, light pen, joystick etc.

·         It does not support multimedia environment.

·         It does not support multitasking, multiprogramming, multithreading etc.

Advantages 

·         It is efficient in program execution than GUI based operating system. 

·         Faster in execution, hence it is used in mission critical server system. 

·         Burden for CPU is less because it executes commands only not graphics. 

·         CUI based operating system can runs on simple configuration or old computer too. 

·         CUI based operating system are cheap or available free on the web. 

·         It requires less memory space.

Disadvantages

·   It difficult to use for general users because number of commands should be memorized. 

·         Pointing devices cannot be used for selection and manipulation of commands. 

·         It simply black or white backer and text on it.

·         It does not contents graphical components such as icon, menu etc.

·         It is less user-friendly.

b)      GUI (Graphical User Interface)

Graphical User Interface (GUI) operating system presents commands in graphical form. For example, application programs, commands, disk drives, files etc. are presented in the form of icons. Usually a command is given to the computer by clicking with mouse on the icon. GUI also provides menus, buttons and other graphical objects to the user to perform different tasks. GUI is very easy to interact with the computer. GUI is not an operating system, but rather an interface design on your computer, so computer that you use has a more attractive appearance. Examples of GUI operating systems are Windows, Linux, and Solaris. 

Features of GUI

·         GUI is graphical and user friendly.

·         It is easy to learn and operate.

·         No need to remember syntax and commands.

·         It requires large amount of memory space.

·         It supports graphics components such as text box, icon, desktop etc.

·         It also supports all types of pointing devices.

·         It needs faster processor to operate.

·         GUI based OS are usually 32 or 64 bits operating system.

·         It supports multimedia environment.

·         It support multitasking, multiprogramming, multithreading etc.

·         It is slower than CUI based OS.

Advantages

 It can be user-friendly and speed up the user's work.

 It can be more attractive for non-technical people.

No need to remember syntax and commands.

Disadvantages 

·         it generally requires more memory resources

·         it might require the installation of additional software

·         It requires more memory space in RAM and HDD.

Differentiate between CUI and GUI OS

GUI	CUI
It is based on graphical user interface mode	It is based on command user interface mode
It supports multi user, multiprocessing, multiprogramming environment.	It supports only single user environment.
It is graphical and user friendly.	It is more textual and less user friendly.
It is easy to operate and learn.	It is difficult to operate and learn.
Instructions are given using graphical components like menu bar, toolbar etc.	Instructions are given using character.
It is very common.	It is less common.
Here, we can preview the contents before print.	Here, impossible to preview the content like GUI.
It supports number of input devices such as keyboard, mouse, joystick etc.	It supports only keyboard.
It requires more memory space in RAM and HDD	It requires less memory space in RAM and HDD
It is slower execution than CUI.	It is faster execution than GUI
E.g. windows os, Vista, LINUX etc	E.g. MS-DOS, PC-DOS etc.

Based on the mode of user

Single user

               A single user operating system provides facilities to be used on one computer by only one user. Normally, one user program is only allows to be run and processed at a time. So, there is no multiprogramming of user programs. It is based on small microcomputer which allows a single user to operate the machine. Examples are MS-DOS, PC-DOS, Windows 95, Windows NT, Windows 2000, windows 7, Mac  etc.

Multi user

             A multi-user operating system has been designed for more than one user to access the computer at the same or different time. It allows two or more users to run programs at the same time. The OS of mainframes and minicomputers are multi-user systems. Examples are UNIX, LINUX etc.

Disk Operating System(DOS)

DOS

DOS (Disk Operating System) was the first widely-installed operating system for personal computers. It was the most popular before coming ms-windows os. It is developed for the disk drives. It is a CUI based os. Its main function is to establish the relationship between hardware and software. It also provides an executable environment to the software inside the system. E.g. PC-DOS, MS-DOS, DR-DOS, Free-DOS, ROM-DOS and PTS-DOS. etc.

·         The first personal computer version of DOS, called PC-DOS, was developed for IBM by Bill Gates and his new Microsoft Corporation.

·         He retained the rights to market a Microsoft version, called MS-DOS.

Features of DOS

·         It is single user and single tasking os.

·         It is a 8-bits to 16-bits os.

·         It is CUI based os.

·         It has two types of command such as internal and external.

·         The file name under DOS must not be more than 11 characters.

·         It supports less number of i/p devices.

·         It does not support graphical interface.

MS-DOS (Microsoft Disk Operating System)

MS-DOS is a command based single user, single tasking operating system software which is an extended version of CP/M. It was created for IBM PC and 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.

Features of MS-DOS

·         It is single user and single tasking os.

·         It supports both HDD and FDD.

·         It supports various languages.

·         It is a CUI based OS.

·         It managing easy filing environment.

·         It also supports the hierarchical file system.

·         It supports the dynamic file allocation.

Types of MS-DOS command

There are two types of MS-DOS command:

INTERNAL COMMANDS

·         These are those commands which are contained in command.com files of MS-DOS.

·         They are loaded to the main memory during the time of booting.

·         It is executed from DOS prompt.

·         These are those functions that are built into the command interpreter.

·   There is no need of any external file in computer to read internal MS-DOS command.

·         These commands can be used as long as DOS is running on the system.

·         Internal commands do not vary from system to system.

·         These are ver, time, del, md, cd, copy con, cls, date, vol, ren, copy etc.

EXTERNAL COMMANDS

·         These are those commands which are not in-built in MS-DOS.

·         They are stored on the system disk as program files.

·         These commands are not loaded at the time of booting.

·         They are only loaded to the memory when they are used.

·         External commands are those which are not included in the interpreter.

·    There is a need of an internal file in the computer to read external MS-DOS command.

·     External command may vary from system to system. This means any two computers with same version of MS-DOS may have same internal commands, but may have different external commands.

·         These are tree, xcopy, diskcopy, more, print etc.

Concept of File

A file is a collection of related information stored on a disk. Each file is referred by a unique name called file name. File names are divided into two parts, first part is called primary file name and the second part is called the extension which are separated by a period or dot.

Types of file

·         Program or executable file (.exe, .com, .bat)

·         Graphics file or picture files (.bmp, .jpg, .gif)

·         Data file( .dat, /mdb)

·         Text file (.doc, .txt, .ini)

General rules for naming/ writing the file name:

·         File name can be up to eight characters.

·         File extension can be up to three characters.

·         File names must not contain: blank spaces, commas, backslash, dot etc.

·         Never makes this name of file: CLOCK$, CON, AUX, COM1, COM2,COM3, COM4, LPT1, LPT2, LPT3, NUL, PRN etc

·         Blank spaces are not allowed in the mid of file name.

·         File name must begin with alphabet or letter.

·         File name is combination of letters, digits and special symbols.

·         Some special symbols are also used such as @, #, $, %, ^, _, ~, {}, -, ‘, () etc

·         It is not case sensitive in most of the OS.

·         Examples are: Nepal.txt, kic.doc, lab.bmp, list.xls etc

Extension

It helps us to understand the file type. After the filename no need to type the extension because extension is supplied by the software package automatically to identify the application used.

Directory

A directory is a partition place or table content of a disk which is used for storing files and sub-directories. A directory contains the files with detail information such as name, size, address, date of creation, last date of modification, etc.

There are two types of directories:

·         Root directory: - Root directory is the main directory of disk which contains many other directories and files. It is also called parent directory. Disks have at least one directory which creates itself when a disk is to format that is called root directory. Root directory is indicated by back slash (\).

·         Sub directory: - A sub directory is a directory inside another directory. A sub directory is also called child directory. Sub directory can contain other directories and files inside it.

Wild card characters

A wildcard is a symbol used to replace or represent one or more characters in file name, extension, character, directory, drive etc. it is used for quick execution of the DOS commands. Basically, the wild cards are ‘?’ and ‘*’. The wild card characters are:

·         *  ->  represent a group of known characters such as file name, extension

·         ? -> Indicate any one character.

·         .* -> represent unknown extension.

·         *.* -> represent any unknown file name with any extension.

·         ^ -> represent control sign

·         >  -> represent a prompt component separator/ direction

·         / -> adding options/ switch

·         \ -> represent a root directory and directory separator

·         : -> represent a drive component

·         | -> Pipe line

Some examples of wild-card characters:

·         Dir*.doc :- display all files having doc extension.

·         Dir r*.xls :- displays all files starting with r and having xls extension.

·         Del*.chk :- delete all files having chk extension.

·         TT?.exe :- Represents all typing tutor application.

·         Dir/ON/P :- displays all files and directories in ascending order page by page.

·         CD\ :- to return back from the existing directory into the main prompt.

·         A: or C: :- changing drive.

·         C:\> :- Main prompt

·         Dir???.bas :- displays all files having three character in filename and bas as extension

·         dir he??.* :-. List any file that is four characters long, begins with he, and has any extension. For example, help.txt, help.mp3, and heck.jpg would all be matched.

·         rename *.txt *.jpg :- Rename all files in the current directory that end with the file extension .txt to .jpg. For example, the file test.txt would become test.jpg.

·         del comp*.txt :- Deleting files in MS-DOS that begin with comp and end with a .txt extension.

Definition of: DOS path name

The path name is used whenever it is necessary to type in the location of a file rather than pointing to it with the mouse. The path starts with the drive letter followed by the directory hierarchy and ends with the file name itself.

pathname

Specifies a pattern, file or directory.

For example:

DRIVE     DIRECTORIES     FILE NAME

This is often called the "full path name," which defines the entire route, or path, to a specific file.

The following example is the full path name to the SALES.DBF file that resides in the DBASE directory on the C: drive:
c:\dbase\sales.dbf

The full path to a file named BUDGET.WK1 in the root directory on the D: drive looks like this:
d:\budget.wk1

Sometimes, you cannot tell whether a path name is a directory path or a full path name to a file. The following example could be both. LETTER could be a subdirectory attached to the WP directory, or it could be a document within the WP directory.
c:\wp\letter

If LETTER was a document in the LETTER directory, its full path name would be:
c:\letter\letter

Filename

    A filename (also written as two words, file name) is a name used to uniquely identify a computer file stored in a file system. Different file systems impose different restrictions on filename lengths and the allowed characters within file-names.

A filename may include one or more of these components:

·         host (or node or server) – network device that contains the file

·         device (or drive) – hardware device or drive

·         directory (or path) – directory tree (e.g., /usr/bin, \TEMP, [USR.LIB.SRC], etc.)

·         file – base name of the file

·         type (format or extension) – indicates the content type of the file (e.g. .txt, .exe, .COM, etc.)

·         version – revision or generation number of the file

Booting

Booting is a process of loading the system files (IO.SYS, COMMAND.COM and MSDOS.SYS) into the memory from bootable disk like as HDD, CD, DVD, FDD etc.

Types of booting

a)      Cold Booting: - A process of starting the computer from off-state is known as cold booting. In cold booting period, the computer can perform following tasks:

§  Read the RAM space.

§  Read the ROM instructions.

§  Checking all the internal components of the computer system.

§  Loading the system files into main memory.

b)      Warm Booting: - A process of restarting the computer from on-state is called warm booting. In the warm booting period, the computer can perform following tasks:

§  No read the RAM space.

§  No read of the ROM instructions.

§  No checking internal parts of computer system.

§  Only, loading the system files into memory.

Note: - press ctrl+alt+del for reboot the computer only in windows-95.

Remember:

The Minimum requirements for booting to start, we need at least three files

a)      ms_dos.sys

b)      IO.SYS

c)      Command.com

In both files the ms_dos.sys file is a hidden file and the Command.com is a regular file.

MS-DOS System files

a)      IO.SYS:- It is a hidden file in the root directory of the primary drive. This file provides the basic I/O capability for the system, allowing it the ability to communicate with the different peripheral.

§  It permanently resides in the memory as long as the power is ON.

§  It interacts between ROM BIOS and call from the MSDOS.SYS program.

§  It is always contains at least five device drivers, used to control the operation of our keyboard, screen, printer, disk controller and system clock.

§  Its final task is to load COMMAND.COM.

b)      MSDOS.SYS:- it is also a hidden file in the root directory sometime called the kernel for DOS. When an application needs to access a device or peripheral, this file translates the request into action that IO.SYS can perform.

§  This file interacts directly with application programs and IO.SYS.

§  It acts as a bridge between application programs and IO.SYS

c)      COMMAND.COM: - it is the command interpreter file. It can accept command from the user, launch programs and pass this information to MSDOS.SYS.

§  It interprets the internal command of MSDOS directly to the CPU and the internal command to the CPU after reading the external command files.

§  It is also called command processor.

§  It also produces the DOS disk prompt, performs error checking, and display error messages when system error are detected.

d)     CONFIG.SYS: - It is a system configuration file. It contains commands for configuring computer’s hardware components (memory, keyboard, mouse, printer etc) and reserved space in memory for processing of information.

§  When the computer is switched ON, it looks for a file named CONFIG.SYS. if DOS finds that file, it configures the system according to commands given in this file.

§  It contains two types of commands: configuration command and device driver command.

§  Loading up device driver software.

§  Configuring files, buffers and application program.

§  Installing memory resident program.

e)      AUTOEXC.BAT:- It is another user-configuration text file that I used to set a system. It sets DOS prompt, searches files for executable files and tart memory resident program and makes our work convenient.

§  These commands are executed automatically in sequence at the time of booting of computer since this file is executed automatically at the time of booting of computer.

Drive and Drive letter

All the secondary storage devices like floppy disk, hard disk and compact disk are called drive.

All the storages are denoted by different alphabets and letters followed by colon(J, which are called drive letters.

Example

Drive                                       Drive letter

Floppy Drive                           A: or B:

Hard Disk                               C: or D: or E: or F: etc (if partitioned)

DOS Prompt

It is the main gate of the MS-DOS, from where we can do any type of work. It is denoted by A:\> or C:\> or D:\>, or E:\> etc.

Working or current directory

The directory which is currently used read/ write process is called working directory or current directory.

Windows

Windows is multi user; multitasking and GUI based operating system which is developed by Microsoft Corporation, USA. It allows a user to open multiple programs at a time in separate windows. Nowadays, windows OS is used in PC, including home and business, desktops, laptops, notebooks, media centers. Almost 90 % of all personal computers use this system.

Features of Windows OS

·         It is GUI based OS.

·         It is easier to learn and use.

·         It allows the user to work on a number of applications simultaneously.

·         Failure to any application does not harm the computer.

·         It has many built in programs.

·         It has fast processing capability.

·         It helps to run the multiple applications at a time.

·         It is more user-friendly.

·         It is 32 bits, 64-bits and 86-bits OS.

·         It supports multiple numbers of i/o devices.

Choices of Operating System

DOS

Acronym for “Disk Operating System”. DOS is a 16-bit, single-user operating system that does not support multi-tasking. It is far easier to administer than UNIX, but less powerful. Compared to graphical interfaces such as Windows and Mac OS X, it's also not particularly user-friendly.

Microsoft Windows Operating System

The Windows operating system is developed and maintained by Microsoft, the company founded by Bill Gates. The first version was released in 1985. Since then, it has grown significantly, and it now dominates the market. Windows uses a graphical user interface to make it easier for people to use their computers. The primary ways that people navigate are through icons on the desktop and the Start menu.

The Windows operating system, like the Macintosh and Linux, allows people to manage files and run software programs on desktop and laptop computers.

Open source

Open source refers to a program or software in which the source code (the form of the program when a programmer writes a program in a particular programming language) is available to the general public for use and/or modification from its original design free of charge. Open source code is typically created as a collaborative effort in which programmers improve upon the code and share the changes within the community. Example: unix, linux etc

UNIX

UNIX (pronounced as YOO-niks) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Lab. UNIX runs on many types of computers, including supercomputers, notebook PCs, mainframes and minicomputers. Its main ability is that it works with so many kinds of hardware.

Bell Labs distributed the operating system in its source language form, so anyone who obtained a Copy could modify and customize it for his own purposes. By the end of the 1970s, dozens of different versions of UNIX were running at various sites.

Types of UNIX

There are many different versions of UNIX, although they share common similarities. The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.

Here in the School, we use Solaris on our servers and workstations, and Fedora Linux on the servers and desktop PCs.

The UNIX operating system

The UNIX operating system is made up of three parts; the kernel, the shell and the programs.

The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the file store and communications in response to system calls.

The shell

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).

Files and processes

Everything in UNIX is either a file or a process.

A process is an executing program identified by a unique PID (process identifier).

A file is a collection of data. They are created by users using text editors, running compilers etc.

Examples of files:

§  a document (report, essay etc.)

§  the text of a program written in some high-level programming language

§  instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);

§  a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.

LINUX

Linux is a generic term that commonly refers to Unix like computer operating system that use the Linux kernel. Linux is one of the most prominent examples of free software and open source development; typically all the underlying source code can be used, freely modified, and redistributed by anyone.

Ubuntu, NepaLinux, User Linux etc are few examples of Linux distributions.