System file

A system file in computing is a critical computer file without which a computer system may not operate correctly. These files may come as part of the operating system, a third-party device driver or other sources. Microsoft Windows and MS-DOS mark their more valuable system files with a "system" attribute to protect them against accidental deletion. (Although the system attribute can be manually put on any arbitrary file; these files do not become system files.)

Specific example of system files include the files with .sys filename extension in MS-DOS and Windows, the System suitcase on Mac OS and the files located in sys, the root folder of the Linux file system, sysfs.