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. is loaded by the DOS BIOS  as part of the boot procedure. By default, the file is located in the root directory of the bootable drive/partition and has  attributes so it cannot be deleted or executed easily.

The DOS kernel in some OEM releases of MS-DOS have different names, such as  and. IBM PC-DOS as well as DR-DOS since 5.0 (with the exception of DR-DOS 7.06) used the file, whereas DR-DOS 3.31 to 3.41 used   instead. FreeDOS uses  (DOS BIOS and kernel combined). The name of this file is not important as long as the boot sector contains its name.

Windows 9x
In Windows 95 through Windows Me, the DOS kernel has been combined with the DOS BIOS into a single file,  (aka  ), while   became a plain text file containing boot configuration directives instead. If a  file exists, the system will retrieve these configuration directives from   rather than from. Some DOS utilities expect the  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   configuration file since Windows 95.