Operating Systems - Customising DOS

The DOS start-up procedure is defined in the autoexec.bat and config.sys files located in the root of your "C:\" drive. We highly recommend making back up copies of these files before modifying them.
To deactivate a line of command in either file just place the "rem" (remark) command at the beginning of the line, there is no need to delete the entire line.


The config.sys file is a text file which loads device drivers and defines parameters for MS-DOS.

  • device is used to load device drivers
  • devicehigh loads the driver into the high memory area
  • dos defines the area of memory where DOS will be loaded
  • drivparm defines disk drive specifications
  • fcbs specifies the number of file control blocks
  • files specifies the number of files that can be opened at the same time
  • install runs a resident program (TSR - terminate and stay resident)
  • lastdrive defines the number of valid disk drives
  • shell indicates that another command prompt other than COMMAND.COM should be used.
  • stacks specifies the amount of memory reserved for hardware interrupts


The autoexec.bat is a batch file (as denoted by the file extension), a text file which contains a group of commands run one after the other, each command is written on a separate line.
Some of the following are examples of commands that can be added to the autoexec.bat (any program that runs in DOS can be added to this file):

  • the path command tells MS-DOS the file location where files can be accessed when in another folder.
  • the prompt command sets the type of MS-DOS prompt
  • the doskey command allows you to use the directional keypad to go back through previous commands that have been run.

Creating a start menu

In DOS, Windows 95 or Windows 98 systems it is possible to create a start menu where you can select which devices are to be loaded in DOS and even (as is the case with Windows 95/98) tell the system to start-up in either Windows or DOS. The config.sys and autoexec.bat files (and in Windows the msdos.sys file) must be modified to allow the selection of DOS and Windows at start-up.

Modifying the config.sys file

To have the Windows and DOS options on start-up, the config.sys file must be modified as follows:


REM *********Start Menu*************************************
MENUITEM=2, Windows 98
REM ***********OPTIONS*************************************************

contents of the config.sys file you wish to use in configuration 1

contents of the config.sys file you wish to use in configuration 2

explanation of changes made to the config.sys file

[COMMON] contains file information config.sys which is common to both configuration 1 and 2.

[MENU] contains the titles of the menu items (here DOS and Windows 98) as well as the menu settings:

  • background color (here 15) and text color (here 0)
  • the item (here the 2nd item) is loaded if no item is selected after a set time (here 4 seconds)

Then both configurations after the markers [1] and [2]

modifying the autoexec.bat file

The autoexec.bat file must be modified as follows:

goto %config%

autoexec.bat file contents for configuration 1
goto end
autoexec.bat file contents for configuration 2
goto end
(items common to both configurations)
explanation of changes made to the autoexec.bat file

The changes made to the autoexec.bat file are not complicated, there are two sections in the file which the system will go to as you previously selected in the config.sys (as the system will execute the config.sys first).

modifying the msdos.sys file

If you wish to choose between DOS and Windows you must edit the msdos.sys file. Make sure you remove the read-only attribute, then add or modify the following lines:


then add the line "win" to the end of the configuration corresponding to Windows in the autoexec.bat, which will then load Windows if selected.

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This document, titled « Operating Systems - Customising DOS », is available under the Creative Commons license. Any copy, reuse, or modification of the content should be sufficiently credited to CCM (ccm.net).

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