A text file containing special system configuration commands, found in the root directory on an MS-DOS computer, typically on drive C (the hard disk). It is read by MS-DOS at boot time, after the setup has been read from CMOS RAM and before running AUTOEXEC.BAT. It can be modified by the user.
Some example commands which CONFIG.SYS might contain are:
Load the expanded memory manager.
DOS is located in UppeMemoryBlock.
Set the number of file control blocks.
DEVICEHIGH /L:1,12048 =C:\DOS\SETVER.EXE
Set the country code for some programs.
SHELL=C:\DOS\COMMAND.COM C:\DOS\ /E:1024 /p