DOS

1. What is an Operating System ?

An Operating System is a set of programs that controls and coordinates the use of computer hardware among various application programs. It provides an environment within which user can execute programs. A computer can be divided into four components : the hardware, the operating system, the applications programs, the users. It is the operating system that manages all the above components. The various functions of the operating system are :

• Controlling Input/Output devices (Keybd, Mouse, Monitor, Printer, Plotter etc..)


• Memory and File storage management


• CPU Scheduling and controlling processes


• Loading, initiating, executing and supervising user applications programs


• Handling errors and restarting


• Providing command interface between user and computer system

Examples of Operating system are : UNIX (Solaris, IRIX, HPUnix, Linux, DEC Unix) Microsoft Disk Operating System (MS-DOS), WIN95/98, WIN NT, OS/2 etc.

2. Introduction to DOS / WINDOWS

Though UNIX was a powerful operating system available, but it was not suitable for 8-bit 8086 microprocessor based Personal Computers. So there was a need for a small operating system that could work in 640K memory(RAM). DOS was an variant of CP/M (Control Program/Monitor) which ran for the first time on IBM-PC in 1981. It is called so because it resides on Floppy or Hard disk and provides command level interface between user and the computer hardware. The different versions of MS-DOS have evolved over a period of time with Microsoft introducing new features in each new releases. Starting with MS-DOS1.1, the latest version was MS-DOS6.22 released in 1994. There are various versions of DOS like MS-DOS(Microsoft), PC-DOS(IBM), Apple DOS, Dr-DOS etc.

WINDOWS was similar to APPLE Mach operating system interface on IBM-PC. The main features of windows are easy to use graphical user interface (GUI), device independent graphics and multitasking support. The first version of windows1.0 was introduced in 1985. Windows was an application of MS-DOS using the basic commands of DOS. Windows for Workgroup (WIN3.11) released in 1992 was an integrated windows and networking package with file and printer sharing capabilities, a network mail (Microsoft Mail) and a workgroup scheduler (Schedule+) packages in windows environment. WINDOWS-95 released in 1995 is a 32-bit operating system which includes MS-DOS7.0 and takes control of computer system after starting.

The main features of WINDOWS-95 are:

• Windows 95 is easier to learn and use than any of its predecessors.


• Windows 95 and its applications run under the PCs protected mode, which mean that one ill behaved program cannot compromise the memory and resources of another. This approach adds a large measure of reliability to the total operating environment. The crash of a single errant program does not automatically crash the operating system or any of other programs that your running.


• Windows 95 is a pre-emptive multitasking means that programs running in the background do not significantly degrade the interactive program that you are running in the foreground e.g. you can comfortably type into word processors while your database system backs up all its files. Under Windows 3.1 the typed key displays lagged behind while the backup procedure logged the processor.


• Windows 95 integrates virtually all of your computing tasks and resources like networks, E-mail, multimedia, system administration, printing, faxing, applications into one common user interface.

3. What is BOOTing ?

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.

4. 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.

5. 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.

6. 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.

7. Disk/Drives :

The user can store data or programs on secondary storage devices called Hard disk or Floppy disk. Physically disks store data by recording any pattern of magnetic changes on using a tiny read-write head that moves over the surface. Disk is divided into sectors and tracks. The first two characters of alphabet (a: or b:) are reserved for Floppy disks, Hard disks are identified by characters (c:) or (d:), the next character in the sequence is assigned to Compact Disk (CD-ROM) drive further the network drives connected to the system are assigned the remaining characters.

8. Directory :

It is a special type of file that contains other files. The relation between files, directories and disk is very similar to the relation between papers, filing folders and filing cabinets. The hierarchy in which directories are kept is called a tree structure.

9. Definition of a file : File Names

Information or data is stored is stored on a disk in the form of a file. When storing any file, it must be given a unique name, which can be used for subsequent identification/reference. Filenames should not be longer than 8 characters, can have an extension which should not be longer than 3 characters. Following characters are valid in a filename : A to Z , a to z, 0 to 9, !,@#$%&(){}_-\’. Different files are identified by their extensions. File which have extension EXE, COM, BAT are executable files. They can be executed by just typing their name at the command prompt. Extensions TXT, DOC, BAK, BAS, C represent text file, Documentation (MS-Word) file, Backup file, basic program file, C program file respectively.

10. Wildcards Definition

To retrieve and identify file, we can use its specific name or may refer to it with the help of wildcards which can even refer to entire group of files. There are two wild card symbols : asterisk (*) indicates that any or a one valid character can occupy that position or of the remaining positions in the filename or extension, Question mark (?) means that any one valid character can occupy that position.

11. 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.

12. Types of DOS 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 he system prompt(C:\>) level. To use these commands no extra /external file is required. E.g. DATE, TIME, DIR, VER 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.

13. BASIC DOS COMMANDS :

a) Directory Commands :

DIR : To list all or specific files of any directory on a specified disk.

MD : To make directory or subdirectory on a specified disk/drive.

CD or CHDIR : Change DOS current working directory to specified directory on specified disk or to check for the current directory on the specified or default drive.

RMDIR or RD : Removes a specified sub-directory only when it is empty. This command cannot remove root directory (C:\) or current working directory.

TREE : Displays all of the directory paths found on the specified drive.

PATH : Sets a sequential search path for the executables files, if the same are not available in the current directory.

SUBST : Substitutes a string alias for the pathname and creates a virtual drive.

b) File Management Commands :

COPY : Copies one or more files from source disk/drive to the specified disk/drive.

XCOPY : Copies files and directories, including lower-level directories if they exists.

DEL : Removes specified files from specified disk/drive.

REN : Changes the name of a file(Renaming).

ATTRIB : Sets or shows file attributes (read, write, hidden, Archive).

BACKUP : Stores or back up one or more files/directories from source disk/drive to other destination disk/drive.

RESTORE : Restores files that were backed up using BACKUP command.

EDIT : Provides a full screen editor to create or edit a text file.

FORMAT : Formats a disk/drive for data storage and use.

c) General Commands :

TIME : sets or displays the system time.

DATE : Sets or displays system date.

TYPE : Displays the contents of at the specified file.

PROMPT : Customizes the DOS command prompt.

If a users requires help on any DOS commands he/she may type help and command name at the command prompt.