Overview of Disk Operating System (DOS)

Disk Operating System

DOS stands for Disk Operating System. It is a product of Microsoft Corporation released in 1980. DOS is a single user, single task character based operating system where user will perform only single task at a time. DOS is called C.U.I meaning character user interface contrary to Graphical User Interface (GUI) in Windows OS. Being solely C.U.I user can view and enter only characters in this operating system that is on disk. DOS fetches itself to system area and data area. System area consists of boot area, FAT area and root directory.C:> is called C prompt

A:> is called A prompt.

C:>_ After the prompt there is a blinking symbol called cursor. It shows that it is waiting for DOS commands.

The following are considered as the main files for DOS:

  1. IO.SYS (Input and Output)
  2. MSDOS.SYS (Microsoft DOS)

IO.SYS file

IO.SYS is an executable binary file and is essential part of MS-DOS containing the default MS-DOS device drivers (hardware interfacing routines). It is the first system file loaded into the RAM. This file stores the input and output device functions.


MSDOS.SYS is an important system file on MS-DOS containing core operating system code that runs after IO.SYS file. This is the second system file that is loaded into the RAM. This file is used for store and access of data.


COMMAND.COM is the filename of the default operating system shell for DOS operating systems and is the third system file that’s loaded into the RAM. DOS commands are executed with the help of this file.

Leave a Reply

Your email address will not be published. Required fields are marked *