When performing an exit to DOS, by pressing the Start-button and selects the Shutdown...-option to Restart the computer in MS-DOS mode, then it checks the properties of a special file called Exit to DOS.pif:

• By the default the properties are set to Use Current MS-DOS Configuration, and it will exit Windows and execute DosStart.bat (In the Windows folder)
• If the properties are set to Specify A New MS-DOS Configuration, then it will use the Autoexec.bat and Config.sys specified by Exit to DOS.pif

The batch file DosStart.bat can be used to contain all the drivers and settings which usually resides in Autoexec.bat and Config.sys. CD-Rom drivers and other device drivers can be loaded by using the utility Dynaload. It will make the Windows startup faster when only loading DOS drivers at Windows exit.

More Info MS KB134400
More Info MS KB135174
More Info MS KB138996
More Info MS KB141308