File attributes are a type of meta-data that describe and may modify how files and/or directories in a filesystem behave. Typical file attributes may, for example, indicate or specify whether a file is visible, modifiable, compressed, or encrypted. The availability of most file attributes depends on support by the underlying filesystem (such as FAT, NTFS, ext4) where attribute data must be stored along with other control structures. Each attribute can have one of two states: set and cleared. Attributes are considered distinct from other metadata, such as dates and times, filename extensions or file system permissions. In addition to files, folders, volumes and other file system objects may have attributes. DOS and Windows Traditionally, in DOS and Microsoft Windows, files and folders accepted four attributes: Archive (A): When set, it indicates that the hosting file has changed since the last backup operation. Windows' file system sets this attribute on any file that has changed. Backup software then has the duty of clearing it upon a successful full or incremental backup (not a differential one). Hidden (H): When set, indicates that the hosting file is hidden. MS-DOS commands like dir and Windows apps like File Explorer do not show hidden files by default, unless asked to do so. System (S): When set, indicates that the hosting file is a critical system file that is necessary for the computer to operate properly. MS-DOS and Microsoft Windows use it to mark important system files. MS-DOS commands like dir and Windows apps like File Explorer do not show system files by default even when hidden files are shown, unless asked to do so. Read-only (R): When set, indicates that a file should not be altered. Upon opening the file, file system API usually does not grant write permission to the requesting application, unless the application explicitly requests it. Read-only attributes on folders are usually ignored, being used for another purpose. As new versions of Windows came out, Microsoft has added to the inventory of available attributes on the NTFS file system, including but not limited to: Compressed (C): When set, Windows compresses the hosting file upon storage. For more information, see . Encrypted (E): When set, Windows encrypts the hosting file upon storage to prevent unauthorized access. For more information, see . Not Content-Indexed (I): When set, Indexing Service or Windows Search do not include the hosting file in their indexing operation. Other attributes