MSDOS.SYS

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MSDOS.SYS an important system file on MS-DOS and Windows 9x systems. It is run after IO.SYS. In MS-DOS, it contains the core operating system code, the kernel. On Windows 9x systems the DOS kernel code is merged into IO.SYS and MSDOS.SYS is an ASCII file containing configuration directives.

By default the file is located in the root directory of the bootable drive (normally C:\) and has the hidden, read-only and system file attributes set.

DR-DOS and PC-DOS systems used the file IBMDOS.COM for the same purpose.

Windows NT-based operating systems (NT 3.1-4, 2000, XP and Vista) do not use the file, as they have a different boot sequence, such as the NTLDR file.