The MSDOS.SYS is a hidden, read-only, system file in the root directory of the boot disk, so you must first turn off these attributes before you can edit the file with an ASCII editor such as Notepad or Wordpad. You can use the Windows Explorer or the command line program ATTRIB to change the file attributes. After saving your changes, you must reset the file attributes and reboot the system for the changes to take effect.
Attrib h r s
Notepad msdos.sys
Attrib +h +r +s
The general format of the MSDOS.SYS file is similar to INI files, with keys listed in sections with section headers given inside square brackets.
[section]
name=value
You may have to add a parameter to the Options section, if the parameter is currently set to the default value and not explicitly listed. Be careful not to add a second parameter line for the same parameter. MSDOS.SYS will typically contain a large number of comment lines containing nothing but lowercase x's. These lines are required in order to make the file size larger than 1024 bytes. Valid information may be stored both before and after these comment lines, so check the file carefully.