Disk Operating System (DOS)

Subject: Computer Science

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This note contains infomation about DOS operating system with its feature. It also contain CUI interface and its character along with internal and external DOS command. At last, we can see the types of system file which are necessary in any OS.
Disk Operating System (DOS)


Ms-Dos is a result of shortening of Microsoft operating system. It is a popular operating system designed by Microsoft corporation for the user of IBM compatible computer and is replaced by its extension of Windows OS. It is a Character User Interface (CUI) or Text Based Interface (TBI), in which all commands and correct meaning have to be remembered and all are in text form.

The main function is to establish the relationship between hardware and software. It also provides an executable environment to the software inside the system. Out of this, it also allows a user to communicate with a computer by all the way by the use of commands called DOS command.

Thus, it is an interpreter between hardware and software and provides the working environment to the users. It also controls the hardware, such as the keyboard, monitor, printer, etc.

Features of MS-DOS:

  • It is the primary type of OS, used before the Windows was developed.
  • It is a 6-bit operating system developed for personal computers.
  • It uses CUI. So, a user needs to provide instructions through the text and internal commands.
  • It uses two types of commands: externals and internal commands.
  • It does not provide graphics facility but, some application programs which runs under DOS and may provide graphics facility.
  • Improved memory management capabilities
  • Hierarchical file directory structure.

CUI (Character User Interface)

The operating system which provides the user with the faculty of entering commands through interactive terminals for initiating program and applications is called CUI OS. CUI based on OS allows a user to type their commands using the keyboard to get computer’s response. The response is to display on the screen .

CUI never call a program running. Under it, we have to give a command to create the folder, copying files, deleting folder, etc. Examples: MS-DOS, PC-DOS.

Characteristics of CUI:

  • They are very difficult to use because the user needs to memorize the command and syntax.
  • Not user operating system.
  • Graphics design and image are presented to the user in the form of a text line.
  • It does not support multimedia and animation.
  • Input and output are provided to the user in the form of a text line.

(Dilli , et al., 2015,159-166)


A file is a collection of related information. It has a name with the extension that specifies a type of file. Executable files are also called Program files and often have an extension like .exe and .com. Examples: practical.doc, where practical is a file name and .doc, is an extension.



Basically, there are 4 types of files. They are:

  1. Program or executable file (.exe, .com, .bat)
  2. Graphics file or picture files (.bmp, .jpg, .gif)
  3. Data file (.dat, .mdb)
  4. Text file (.doc, .txt, .ini)

There are some rules for writing the file name. Such as:

  • The primary filename cannot be more than 8 characters. Example: computer.jpg
  • Extension file name cannot exceed 3 characters. Example: vtae.xls
  • No blank space is allowed between file name and extension.
  • Primary and extension file name are separated by a period dot (.).
  • Punctuation marks; @, $, ^, #, %, can be used for file name. Example: us@125.doc
  • Rest of the other symbols is not allowed to use in a file name.
  • Characters (a-z, A-Z) and numbers (0-9) can be used for a file name.


A directory is a catalog for files stored on the disk of personal computers. It is used for organizing the files on the disk to make it easier to find the files. It contains the names of the files, size, date and time the stamps are created or modified. The root directory is the initial directory of a storage disk. All other directories on that are sub-directories of that root. The root directory is indicated by the backslash (/). A subdirectory is a directory within another directory.

Rules for writing the directory names:

  • Directory name must not exceed 8 characters.
  • The extension can be up to 3 characters.
  • Blank space is not allowed.
  • Both the upper and lower case letter are accepted.

Given figure represent the directories:hjgjh

Wildcard Character

Wildcards are characters that can be used to stand-in for unknown characters in file names. In DOS, wildcard characters can match up with any character that is allowable in a file name. There are two wildcards in DOS:

*: Matches up with any combination of allowable characters.

? : Matches up with any single allowable character.

The asterisk character '*' can stand in for any number of characters.

Some example of this command:


This command would delete every file with the doc extension from the root directory of C:

The question mark wildcard, ? stand in for any single character.

Some example of this command:


This command would only delete files that had a single character a.doc or 1.doc is history, but a file like io.doc is perfectly safe as it has two characters.

System files

This operating system has three essential files and many command files for booting the computer system. The files are:

  • SYS: This file let the DOS communicate with hardware through the BIOS. It provides the basic capabilities of I/O. SYS direct the overall process of loading the OS.

  • MS-Dos.SYS: This is the program used by application programs. It contains special subprograms to make common operations easy for the programs. It runs after the IO.SYS. It contains the core operating system code called kernel.

  • com: This file accepts and understands the common that enter using the above two files to give desired results. It is the command interpreter.

  • Sys: Config.sys is a kind of text file containing special Dos commands that tell the OS how the component so that MS-Dos and application can use them.

  • BAT: All the programs that are supposed to run at startup are called BAT. It is a file used to run initialization programs and command that, we would normally type each time we sat on the computer.

(Dilli , 2015,218-222)


Dilli , S. P., Singh, k. E., Khadija , D., Bhatta, K. D., Baral, N., Saud, R. S., . . Dangi, R. (2015). Fundamental of Computer Science. Kathmandu: KEC publication and Distribution.

Things to remember
  • MS-DOS is a popular operation system designed by Microsoft corporation for the user of IBM compatible computer and is replaced by its extension of window OS.
  • MS-DOS is and interpreter between hardware and software, and provides working environment to the users. It also controls the hardware, such as keyboard, monitor, printer, etc. 
  • The operating system, which provides the user with the faculty of entering commands through interactive terminals for initiating program and applications, is called, CUI OS. 
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.

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