MSDOS.SYS

MSDOS.SYS is a vital system file on MS-DOS and Windows 9x operating systems.

In versions of MS-DOS from 1.1x through 6.22, the file comprised the MS-DOS kernel and is responsible for file access and program management. MSDOS.SYS is loaded by the DOS BIOS IO.SYS as part of the boot procedure.