file system definition

Contributor(s): Ellen O'Brien

In a computer, a file system (sometimes written filesystem) is the way in which files are named and where they are placed logically for storage and retrieval.

For example, DOS, Windows, OS/2, Macintosh and Unix-based operating systems (OSes) all have file systems in which files are placed somewhere in a hierarchical (tree) structure. A file is placed in a directory (folder in Windows) or subdirectory at the desired place in the tree structure.

File systems specify conventions for naming files, including the maximum number of characters in a name, which characters can be used and, in some systems, how long the file name suffix can be. A file system also includes a format for specifying the path to a file through the structure of directories.

File system tree
Example of a file tree diagram

File systems and the role of metadata

File systems use metadata to store and retrieve files. Some examples of metadata tags include:

  • Date created
  • Date modified
  • File size

An example of a file system that capitalizes on metadata is OS X, the OS used by Macintosh hardware. It allows for a number of optimization features, including file names that can stretch to character counts of 255.

File system access

File systems can also restrict read and/or write access to a particular group of users. Passwords are the easiest way to do this.

Encrypting files is another way to prevent user access. A key is applied to unencrypted text to encrypt it, or the key is used to decrypt encrypted text. Only users with the key can access the file.

File systems definition evolves

The file systems definition can also refer to the part of an OS or an added-on program that supports a file system. Examples of such add-on file systems include the Network File System (NFS) and the Andrew file system (AFS).

In addition, the term has evolved to refer to the hardware used for nonvolatile storage, the software application that controls the hardware, and the architecture of both the hardware and software.

This was first published in March 2015

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