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.