One of two special text files that the user can create to configure the initial environment of the PC and load special device drivers. CONFIG.SYS is a file stored in the root directory of the disk used to start the PC (usually the hard disk if one is fitted or a floppy in drive A:). If this file is present, then the special commands stored in it are automatically executed when DOS starts up. The other startup file is AUTOEXEC.BAT which contains ordinary DOS commands. This is executed after CONFIG.SYS 


If your PC is already set up, you probably already have an CONFIG.SYS file on your startup disk(s). You can check this with a command such as DIR C:\ CONFIG.SYS. Use TYPE rather than DIR to show the commands that are stored in the file. You should be careful not to delete an existing CONFIG.SYS file or to make inappropriate changes to it as this may prevent software and add-ons from working properly. It is not necessary to have a CONFIG.SYS file. Without one, DOS will set itself up with basic defaults.