tem) A text file that contained commands to load drivers and establish settings in a DOS PC. Along with AUTOEXEC.BAT, it resided in the root folder. CONFIG.SYS was included in Windows versions for DOS compatibility and was replaced with CONFIG.NT in 32-bit versions of Windows starting with Windows NT. Users could easily make changes, and installation programs sometimes modified CONFIG.SYS for their own purposes.
The following CONFIG.SYS example primarily loads memory managers that were essential to squeeze programs into every byte of what little RAM there was at the time. See AUTOEXEC.BAT
device=c:\dos\himem.sys RAM > 1MB
device=c:\dos\emm386.exe ram EMS memory