Config.sys is a file in MS-DOS operating system which is intended to adjust the overall system. Hardware drivers, such as CD-ROM drive, mouse (if any), sound cards, memory managers put into this file to be loaded. Though it ends with. SYS (System), this file is actually a text file with ASCII encoding so that it can be edited easily using a text editor such EDIT.COM, E. EDLIN.COM or EXE. This file is one of the important file in MS-DOS, after the IO.SYS, MSDOS.SYS, and COMMAND.COM.