MS-DOS (Microsoft Disk Operating System)

working fine with latest processors. It is necessary to be installed in the computer. Till windows 3.1, DOS was an individual operating software but now it became a part of windows. It helps to boot the PC. It is a text based single tasking operating software.

MS-DOS manifests each program and piece of task of data as an individual file. Each file has a name, which is stored with the file in the drive. Name breaks down into two parts; the file name and the extension. The file name can be no longer the eight characters and the extension, which is optional, can be up to three characters. No space and other illegal characters like (/ { [ }] + = – ; ? > <) etc can be used in the file name. The file name and extension are separated by a dot (.). Some example of file name and extension are as follows:

The extension tells the type of file. Generally program files has EXE or COM, System files has SYS as extension



DOS has its own system to assign the drives. While booting DOS assign the first floppy drive as A: and second; if installed as B:. Hard drives starts from C: and can continue to Z:; if necessary. DOS defines these letters. Like all OS DOS also creates and uses the same hierarchical directory tree to organize the contents of these drives. A directory is a group of all files. If any directory is created inside any existing directory, the second is called the sub directory.

DOS three main files:

Three main files, accompanied by nearly 80 support files, compose the DOS. These three main files are:

The files are also called the DOS bootable files and must be loaded in the C: drive. IO.SYS handles talking to the BIOS and hardware. MSDOS.SYS is the primary DOS code often called the kernel. COMMAND.COM actually interprets the commands. This file has inbuilt the several commands in it which are known as the internal commands. When we boot the PC in the DOS mode than we get the following screen:

Prompts is a path followed by a > sign. When we get prompt on the screen, we can start to give the commands.

DOS commands:

Being a text based OS, DOS uses commands to complete its tasks. Commands are simply the orders given by the user to do the job with computer. DOS commands are classified into two groups. They are Internal commands and external commands.

Internal commands:

Internal commands are inbuilt in COMMAND.COM which means COMMAND.COM alone can handle these commands. Some commonly used internal commands and their functions are as follows:

1.DIR :- This command is used to display the contents of current directory. When we type this command in the C prompt, we may see something like this:

Example C:>DIR

This command will display the content of C: directory. Several switches can be used after this command. Switches are the conditions to complete the task of command. To find the switches and their uses, type DIR/? in the prompt. This command will display the valid switches and their uses.

2. CLS :- This command is used to clear the screen. When we type the command and press enter than the text of screen will disappear and we will get the prompt only.

Example C:>CLS
3. COPY_CON ( _ sign means

single space.):- This command is to create a new file. If you want to create a file in the DOS, type this command and give the file name.

Example C:>COPY_CON_file name

When we press enter key after giving this command, the cursor will jump to next line where we can start typing our text. After completing the text press Ctrl and Z simultaneously or press F6. The following sign and message will appear telling that the file is saved. This massage shows that the file made by us is properly saved.

4. DEL :- This command is to delete a file from the drive. Deleting a file means removing the file or erasing the file from the drive.

Example C:>DEL_file name

5. COPY :- This command is to copy any file from one location to another. This command only makes the duplicate copy of any existing file.

Example C:>copy_file name_target location

C:>copy_command.com_a: (This command will copy the file in the floppy disk,)

6. MD :- This command is to make a directory.

Example C:>MD_directory name

We can make several directories inside the directory. To make directory inside the directory we have to go inside the directory.

7. CD :-This command will help to go inside the directory. To go inside the directory give the following command;

Example C:>CD_directory name

C:>CD_kamal(The result of this command will be:


8. CD :- This command is to come back to the root directory. If we have to come back to the root directory from any working directory or subdirectory at once type this command.

Example C:KamalAnuArpan>cd


9. CD.. :- This command is to step by step come back to the parent directory.

Example C: KamalAnuArpan >cd..

C: KamalAnu >

10. RD :- This command is used to remove an empty directory. It can not delete a directory heaving any document.

Example C:>RD_direcotory name

Some other internal commands to be practiced in the lab :




External Commands:

External commands not only recognized by COMMAND.COM file. These commands need the individual files to be executed. Internal commands are not enough to complete all the tasks of DOS. So, external commands are designed. Some mostly used external commands are :

1. EDIT :- This command is use to edit any text of DOS. EDIT.COM is the file needed to run this command. If this file is not loaded in the proper location, we can not run EDIT command. When we type the EDIT command in the system prompt, the edit screen appears as follow:

In this screen we can not only type the text but also modify the text, which was already written. To edit any existing file give the command as:


2. FORMAT :- This command is used to format any drive like floppy drive or hard disk drive. Formatting any drive means loosing all the contents of the drive to create new file system. So, before formatting any drive, be sure that the drive does not have any important document. To format any drive type the command as follow:

C:>FORMAT_drive letter(Drive letter like C:, A:, D: etc)

When we press the enter key to format the hard drive than a conformation message display as follow:

3. FDISK :- This command is used to perform the partitioning of a hard disk. Partitioning of a hard disk means creating logical DOS drives on it like C:, D:, E: etc. At least one partition should be created to make a new hard disk working. FDISK.EXE file should be in the disk to run this command. Detail function and process of FDISK will be discussed in the partitioning of hard disk chapter.

4. CHKDSK :- This command helps to check the currently use drive. CHKDSK.EXE file is needed to run this command. When we type this command in the system prompt the above information displays:

5. SCANDISK :- This command is better than CHKDSK because this command checks the drive for error. SCANDIS.EXE file is to be loaded in the disk to run this command. When we type the command the following dialog box will appear in the windows mode. (If the computer is started in the DOS mode this dialog box win not appear. The scandisk will start to scan the disk in the DOS mode) Select the option and click on the START button. First option helps to check the files and folder for error and second option helps to run the standard scanning and surface scanning for error.

6. MOVE :- This command is used to move a file from one location to another. Moving a file is just like cut and paste of MS-Word. MOVE.EXE is the file to run this command.

Example C:>MOVE_file name_target location

7. DELTREE :- This command helps to remove a directory with its contents. DELTREE.EXE is the main file to run this command.

Example C:>DELTREE_directory name

8. SYS :- This command is used to transfer DOS system files from one disk to another. SYS.COM is main file to run this command.

Example C:>SYS A: (This command will transfer the main system files of DOS to floppy disk)

9. ATTRIB :- This command will display or change the attributes of file. Attribute means features of a device or manner in which a variable is handled by the computer. ATTRIB.EXE file is responsible to run this command. Using this command we can make a file read only, hidden or system etc.


Some other external commands to practice in the lab:





Wild-Cards and their functions

Wild cards are commonly used for the quick function of the execution of DOS commands. Wild Cards are just some symbols to represent any character or name. Mostly used two wild cards are asterisk (*) and question mark (?). The combination of wild cards and their meanings are as follow:

Working with some important DOS files:

Being an operating software, DOS includes some important files to manage the computer to run properly. These files are necessary to handle the PC properly. Some important DOS files are:

Echo off



Prompt $p$g

As above if you give the proper command and save your file with .BAT extension, you can directly access the program after typing the file name created by you.

Some terms, their meanings and uses:

1.Booting : Booting is the process to load the main bootable DOS system files from the secondary storage (Hard disk or Floppy disk or Compact disc etc.) to the main memory of computer (RAM). During this process IO.SYS, MSDOS.SYS, CONFIG.SYS and COMMAND.COM files are loaded. These files are enough to run a PC in the DOS mode. Cold booting and warm booting are the types of booting. The first booting is called the cold booting and the booting after pressing Ctrl + Alt +Del or by pressing the restart button is called the warm booting.

2. System prompt : System prompt is a logical sign or symbol to indicate that computer is ready to accept commands. C:> is a sign to indicate the hard disk called the C prompt and A:> is a sign to indicate the floppy disk drive called the A prompt.

3. Volume label : Each disk can have an unique name if given by the user. This name is called the volume label. User while formatting a disk assigns this label. We can easily change the volume label in need.

4. Device : Device is a type of hardware or a physical component. Keyboard, Mouse, Hard disk etc are all individual devices. Peripheral is another name used as synonym of device.

5. Path : Path is just a way. When we have to perform any task than we give the order to complete the task by showing the way.

6. Data : Data are the collection of raw facts. Any types of information we give to computer are known as data. Computer performs its action on this information.

6. Processing : Processing means any types of action taken on the data to get desirable result. Processing is the main job of computer.


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