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.
In Windows 95 (MS-DOS 7.0) through Windows ME (MS-DOS 8.0), 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
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.[nb 1]
IBM PC DOS as well as DR DOS since 5.0 (with the exception of DR-DOS 7.06) used the file
IBMDOS.COM for the same purpose, whereas DR DOS 3.31 to 3.41 used
DRBDOS.SYS instead. FreeDOS uses the file
KERNEL.SYS for the same purpose.
Windows NT-based operating systems (NT 3.1-4, 2000, XP, and 2003) use the NTLDR file and NT 6+ operating systems (Vista, 2008, 7, 8, 8.1, and 10) use bootmgr instead, as they have a different boot sequence.
- The dummy comment in unmodified copies of
MSDOS.SYSexplains these reasons explicitly.
- Robbins, Judd (1991). Mastering DOS 5 (3 ed.). San Francisco, California: Sybex. pp. 68–69.
- "Windows Does Not Start Normally With Bootgui=1 in the Msdos.sys". 2.0. Microsoft. 2013-10-24. KB136416, Q136416. Retrieved 2015-08-20.
- "Contents of the Windows MSDOS.SYS file". 1.4. Microsoft. 2007-01-19. KB118579, Q118579. Retrieved 2015-08-20.
- "How to create an MSDOS.SYS file larger than 1024 bytes". 1.3. Microsoft. 2004-12-21. KB129998, D36528. Retrieved 2014-11-22.
- Kurth, Rüdiger; Groß, Martin; Hunger, Henry (2016-11-29) . "Betriebssystem DCP". www.robotrontechnik.de (in German). Archived from the original on 2019-04-03. Retrieved 2019-04-28.
MSDOS.SYS in Windows 9x (95/98/ME):