MSDOS.SYS is the DOS kernel from MS-DOS 1.x to MS-DOS 6.22, the file is responsible for file access and program management.
MSDOS.SYS is loaded by the DOS BIOS
IO.SYS as part of the boot procedure. By default, the file is located in the root directory of the bootable drive/partition and has
RHSA attributes so it cannot be deleted or executed easily.
The DOS kernel in some OEM releases of MS-DOS have different names, such as
MSDOS.COM. IBM PC DOS as well as DR-DOS since 5.0 (with the exception of DR-DOS 7.06) used the file
IBMDOS.COM, whereas DR-DOS 3.31 to 3.41 used
DRBDOS.SYS instead. FreeDOS uses
KERNEL.SYS (DOS BIOS and kernel combined). The name of this file is not important as long as the boot sector contain its name.
In Windows 95 through Windows ME, the DOS kernel has been combined with the DOS BIOS into a single file,
MSDOS.SYS became a plain text file containing boot configuration directives instead. If a
WINBOOT.INI file exists, the system will retrieve these configuration directives from
WINBOOT.INI rather than from
MSDOS.SYS. Some DOS utilities expect the
MSDOS.SYS file to have a minimal file size of at least 1 KB. This is the reason why a large dummy comment is typically found in the
MSDOS.SYS configuration file since Windows 95.