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Files

In short: Named, contiguous units of data that are stored on a storage medium and managed by a file system.

In more detail: Every file has a name, a location in the file system, metadata (size, modification date, permissions), and content. What kind of data a file contains is often — but not reliably — revealed by the file extension.

In Depth

Every file system organises files in a tree structure of directories (folders), with every file reachable via a unique path (e.g. /home/user/document.txt on Linux/macOS or C:\Users\user\document.txt on Windows). Internally, a file consists of two separate parts: the actual payload data (the byte content) and the metadata, managed separately by the file system — size, creation/modification date, access rights, owner. When renaming or moving a file, usually only the metadata changes, not the content itself.

Some operating systems also distinguish between “normal” files and special cases: directories are technically themselves a kind of file (they contain a list of their entries), symbolic links only point to another file without duplicating its content, and some filenames are reserved (e.g. on Windows, CON, AUX, NUL as historical device names) and can’t be created as a normal file.

See also: File Types