How to Edit the Msdos.sys File If you want to change any of the values in the Msdos.sys file, follow these steps to edit the file: Click Start, point to Find, and then click Files Or Folders. In the Named box, type msdos.sys. In the Look In box, click your boot drive (usually drive C, or drive H if drive C is compressed). Click the Find Now button. Right-click the Msdos.sys file, and then click Properties. Click to clear the Read-Only and Hidden check boxes to remove these attributes from the Msdos.sys file, and then click OK. Right-click the Msdos.sys file, and then click Open With. In the Choose the program you want to use box, click WordPad, and then click OK. Make the changes you want to the Msdos.sys file. When you are done, save the file as a text document, and then quit WordPad. Right-click the Msdos.sys file, and then click Properties. Select the Read-Only and Hidden check boxes to set the attributes for the file, and then click OK. Close the Find window. Restart Windows.