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Disk operating system Essay

MS-DOS (Microsoft Disk Operating System) is a single-user, single-tasking computer operating system that uses a command line interface (CLI).

It also works as an interpreter between user and computer.

The term DOS can refer to any operating system, but it is most often used as shorthand for MS-DOS (Microsoft disk operating system). Originally developed by Microsoft for IBM, MS-DOS was the standard operating system for IBM-compatible personal computers.

The initial versions of DOS were very simple and resembled another operating system called CP/M. Subsequent versions have became increasingly sophisticated as they incorporated features of minicomputer operating systems. However, DOS is still a 16-bit operating system and does not support multiple users or multitasking. For some time, it has been widely acknowledged that DOS is insufficient for modern computer applications.

Microsoft Windows helped alleviate some problems, but still, it sat on top of DOS and relied on DOS for many services. Even Windows 95 sat on top of DOS. Newer operating systems, such as Windows NT and OS/2 Warp, do not rely on DOS to the same extent, although they can execute DOS-based programs. It is expected that as these operating systems gain market share, DOS will eventually disappear. In the meantime, Caldera, Inc. markets a version of DOS called DR-OpenDOS that extends MSDOS in significant ways.

Components of MS-DOS

MS-DOS consists of four essentials programs and a set of additional utilities. Four main programs are
• Boot Record

What is BOOTing ?

It is a process that starts up a computer.
It checks for proper functioning of all the peripheral devices attached with the system. It searches for the operating system and, when located, loads it into the main memory. OR

When the computer is switched on, the firmware program in Read Only Memory(ROM) also called Basic Input-Output System(BIOS) reads programs and data i.e. Operating System and loads it into memory (RAM). This process is known Bootstrapping(Booting). The OS once loaded takes control of the computer, handles user interaction and executes application programs. BOOTing Sequence

During Booting process, computer loads the operating system into its memory. DOS booting involves reading following files into memory namely IO.SYS, MSDOS.SYS, and COMMAND COM.

The Basic Input/Output Program (IO.SYS): This program provides interface between the hardware devices and software of the system. It takes care of the keyboard input, character output to monitor, output to printer and time of the day. The File and Disk Manager Program (MSDOS.SYS) : It contains the file management and the disk buffering management capabilities. It keeps track of all the disk access of an application program and remains permanently in memory.

The Command Processor (COMMAND.COM) : It is also called command interpreter. It is the program that displays the system prompt and handles user interface by executing the command typed in by the user using keyboard. The CONFIG.SYS file : This file contains reference to device drivers which are loaded when OS takes control of the computer. This device drivers are required for configuring operating system for running special devices.

The AUTOEXEC.BAT file : This is a special batch program that is automatically executed when the system is started. It can be used to define keys, define the path that MS-DOS uses to find files, display messages on the screen etc. It will be executed only if it exists in the root directory or the diskette from which the system is loaded. Each time the system is started, MS-DOS executes the commands stored in AUTOEXEC.BAT file. One can run it without restarting the system by typing AUTOEXEC at the command prompt.

Warm and COLD Reboot
Switching on of the computer from Power off and loading the operating system is called “Cold Boot”. This generally starts with memory test and chips initialization. There may be case when the computer is already on or has hanged up and we want to reboot the system. This is known as “Warm Boot” and is done by pressing ctrl+alt+del keys simultaneously or just by pressing “Reset” button on the system.

Naming DOS directories and files

There are two name in DOS and is divided into 2 parts.
1. Primary Name
2. Secondary Name or extension.
Primary name is separated from the Secondary name/ extension with the help of a dot (.) look at the following example.


Primary name can be from 1 to 8 characters long.
Secondary name contains 3 or less than 3 characters and is optional. The extension tells DOS about what kind of file it is.
A valid Character for naming a file are: from A to Z and the digit 0 to 9

Types of DOS commands

C :\> Is known as DOS command prompt, where we give the commands. DOS command divided into 2 parts.
1. Internal Commands or Memory-Resident Commands
2. External Command or Disk-Residence Commands

Any instruction given to the computer to perform a specific task is called command. The DOS has several commands, each for a particular task and these are stored in DOS directory on the disk. The commands are of two types :

(a)Internal Commands : These are in built commands of MS-DOS i.e. these are stored in Command interpreter file (COMMAND.COM). These commands reside in the memory as long as the machine is at the system prompt(C:\>) level. To use these commands no extra /external file is required. E.g. DATE, TIME, DIR, VER etc. These are also called Memory Resident Commands. These commands are automatically loaded into the computer‟s memory during the booting process. They actually included in the Command.com file. So these commands
are executable immediately after getting the DOS prompt.

Example: mkdir, cd, rd, copycon etc.
(b) External commands : These are separate program (.com) files that reside in DOS directory and when executed behave like commands. An external command has predefined syntax. for e.g. HELP, DOSKEY, BACKUP, RESTORE, FORMAT etc. These are also called Disk-Resident Commands. These commands are meant for special purpose. These are found in separate files on Hard Disk or Floppy Disk, hence they don‟t typically consume valuable memory space. They are loaded into memory only when called.

Example: xcopy, move, doskey etc.

Microsoft Disk Operating System

Introduction to the Operating Systems:
An Operating system is software that creates a relation between the User, Software and Hardware. It is an interface between the all. All the computers need basic software known as an Operating System (OS) to function. The OS acts as an interface between the User, Application Programs, Hardware and the System Peripherals.

The OS is the first software to be loaded when a computers starts up. The entire application programs are loaded after the OS. Whenever an application needs information it requests the OS which in turn queries the System clock on the motherboard. User interacts with the computer through the OS then OS interprets inputs given by a user through the Keyboard, Mouse or other input device and takes appropriate actions.

An Operating System can be of Three Types:
Single User

MS-Dos, MS-Win 95-98, Win-ME

Multi User



Novel Netware, Win-NT, Win-2000-2003

1. Single User:

If the single user os is loaded in computer’s memory; the computer would be

able to handle one user at a time.
2. Multi user:

If the multi-user os is loaded in computer’s memory; the computer would be

able to handle more than one user at a time.
3. Network:

If the network os is loaded in computer’s memory; the computer would be able

to handle more than one computer at time.
Command Prompt Interface:
Operating System provides a text based interface called command prompt. From the command prompt commands can be issued to perform file and disk management and to run program. Results of these commands are presented to the user as text message.

C:\>The command prompt can be an alphabet followed by one colon (:), one back slash (\), one greater than sign (>) and one blinking element called cursor (_).

Where C:

represents the Drive letter (Current Drive)


represents the current folder / Directory


represents the end of the Prompt and


blinking element (represents the Cursor)

Always a cursor position decides that the current typed letter from the keyboard will appear on that position.

The operating system (OS) is the first program that must be loaded into the memory of your PC before you can use it for any application. You can start your computer with disk operating system (DOS) or some other operating system such as Windows 95, 97, 98 or Windows NT that might be installed in the Hard disk. In this chapter, we shall discuss the basic facilities available in DOS. Switch to MS-DOS and go through most of the text given in this and the next two chapters.

If your computer is running under windows 95/98 or Windows NT, perform the following steps to switch to MS-DOS, otherwise move to section 2.1. 

Click the start button in the taskbar and press the windows logo key to open the start menu then click programs in the start menu.

Windows displays the program submenu.

In the program menu click MS-DOS Prompt and your screen displays a window that contains MS-DOS Prompt, such as “C:\windows>_”.

If you like you can also restart your computer in MS-DOS mode by using the following steps:
o Close any open programs
o Click the Start Button in the TaskBar or Press the Windows Logo Key to open the Start Menu.
o Click “restart in MS-DOS Mode” and then click OK.
Wait for some time and your PC restarts in MS-DOS Mode.

After your PC starts in MS-DOS Mode or window, skip the next section and move to section 2.2.

What is a File?
In computer terminology, file is a collection of text or data stored on a storage device, such as a Floppy Disk or Hard Disk. If you new to computers, it may sound a bit complicated. Well, a computer file is not much different from a conventional paper file that you must have used, or at least seen being used.

Just as you stored different types of documents (invoice, letters,

reminders, memos etc.) in conventional files, computer files too store information.

File Name
Each file is given a name so that it can be referred to later. This name is called Filename. The filename in DOS can be up to eight alpha-numeric characters long. Optionally it can also have a period (.) followed by an extension name. The extension name the up to three characters long. For instance, consider the following filename:

Here REPORT2 is a filename. This filename does not have an extension name – „DOC‟. The use of an extension name in a filename is optional.

However, the extension name helps in organizing and identifying a file. For instance „DOC‟ may suggest that it is a document file; and „COM‟ may suggest that is a command file. If you use an extension name with a filename, normally you will have to specify the complete file name, normally you will have to specify the complete file name (i.e. including the extension name) while using it with DOS commands. While naming files, you can use the following characters in filename:

A- Z, a- z, 0 – 9, @, #, $, %, ^, &, -, _, { },`, ~,( )

You cannot use other characters, such as coma (,) colon (:), semicolon (;), , \, /, etc. in filename. Moreover, you cannot use space in filenames. Some examples of invalid file names are:



Contains space


Contains more that eight characters

MY, File

Contains commas


Extension name contains more than 3 characters

If you use more than eight characters in the filename or more than three characters in the extension name, DOS may automatically truncate the filename by removing extra characters. Further, some file names, such as COM 1, COM 2, LPT1, com and PRN are reserved by DOS for its own use. Therefore, do not use these names to name your file. Also, remember that all DOS application programs including Word, Excel, WordStar, Bbase III PLUS AND Fox Pro follow the same file naming convention.

WHAT IS A Directory?
As you know, the storage capacity of the hard disk is usually quite large (10 MB to a few GB). You can store hundreds or even thousands of files in your hard disk. Even the capacity of a floppy disk is large enough to store many files. A directory is nothing but a named section of a storage device, such as hard disk, floppy disk. In other words, to organize file on hard disk or floppy disk, these are divided into various segments (sections), called directories.

You can store any number of files in each directory. The directory helps to organise your file in an efficient manner. Using directories in a storage devise is similar to keeping different types of files in an office in separate drawers of a filing cabinet.

For instant, Xyz Company may keep all sales files in the first drawer, all purchase files in the second drawer and all employees‟ files in the third drawer of a filing cabinet. In the same way, when XYZ Company computerizes its operation, it may store all sales files in the SALES directory, all purchase files in the PURCHASE directory and all employees‟ files in the EMPOLYEES directory.

Similarly, the user Raj Kumar may keep his personal files in the RAJ directory and the secretary of XYZ Company may store the letters in the LETTERS or DOC directory.

Like a file name, the directory name can also have up to eight alpha-numeric characters. The directory name can also have and extension name up to 3 characters long. However, normally, the extension name is not used with the directory name.

When you start your PC, it usually responds with „C :/>‟ and selects the main or the root directory of drive C. Any file that you create or copy to drive C is added to this root directory. If you continue to add files in the root directory, after a few days, the root directory will have too many files. This will not only confuse you, it will also make the PC slow. The PC may take too long to locate or open the files if there are too many files in a directory. There for you should try to use directories (and sub directories) in your hard disk

DOS always creates a root directory in each story device. You can create new directories in the root directory of the hard disk or floppy disk. You can store files in these directories. Moreover, beside files, each directory can also have directories. Those, the file and directory organization in DOS looks like the roots of a tree, as show in figure 2.1.here, the root directory in drive C contains if you files in two directories – WORD and EXCEL.

The WORD directory contains a few files as well as a directory TENDER. Sometimes, the second level directory (TENDER in this case) is called sub-directory. The root directory contains another directory – EXCEL. This directory contains a few files as well as two directories – SALES and EMPLOYEE. Both these directories contain files.

At any level in the directory structure, can be created. For example, another directory, say FOXPRO directory may contain files as well as more directories. If you want, you can remove files from any directory or more files to another directory. You can also delete an enter directory. Comments to copy, move, rename and delete files and to create and change directories are discussed letter in this chapter. Additional file and directory comments are discussed in the next chapter.

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