The archive bit is a

file attribute 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. ...

used by

CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...

Microsoft operating systems This is a list of Microsoft written and published operating systems. For the codenames that Microsoft gave their operating systems, see Microsoft codenames. For another list of versions of Microsoft Windows, see, List of Microsoft Windows versions. ...

OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 ...

, and

AmigaOS AmigaOS is a family of proprietary native operating systems of the Amiga and AmigaOne personal computers. It was developed first by Commodore International and introduced with the launch of the first Amiga, the Amiga 1000, in 1985. Early version ...

. It is used to indicate whether or not the file has been

backed up Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The Human feces, stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bo ...

(archived).

Usage

In Windows and OS/2, when a file is created or modified, the archive

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

is set (i.e. turned on), and when the file has been backed up, the archive bit is cleared (i.e. turned off). Thus, the meaning of the archive bit is "this file has not been archived". In CP/M, the meaning is inverted: creating or modifying a file clears the archive bit, and the bit is set when the file is backed up.

Backup software Backup software are computer programs used to perform a backup; they create supplementary exact copies of files, databases or entire computers. These programs may later use the supplementary copies to restore the original contents in the event of d ...

may provide the option to do a

full backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up", w ...

while clearing archive bits – that is, to back up all files regardless of their archive bit status, and to clear the archive bit for all files processed by the backup. This allows for the creation of an initial full backup that will be supplemented by incremental backups in the future. Later, the

incremental backup An incremental backup is one in which successive copies of the data contain only the portion that has changed since the preceding backup copy was made. When a full recovery is needed, the restoration process would need the last full backup plus al ...

task uses the archive bit to distinguish which files have already been backed up, and selects only the new or modified files for backup. The operating system never clears the archive bit unless explicitly told to do so by the user. Even when a user explicitly tells the operating system to copy a file for the purpose of archiving it, the archive bit will still not be cleared. A specific command for clearing or setting the bit must be executed. On the other hand, whenever a file with a clear archive bit is modified (edited), or copied or moved to a new location, the operating system will set the archive bit on the target file. Typically on a

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

that has never been formally backed up, nearly all of the files will have their archive bits set, as there are few applications that make use of archive bits without the user's request. In

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...

as well as nearly all versions of

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

, status of the archive bit can be viewed or changed with the attrib command-line utility, or by viewing the properties of a file with the

Windows shell The Windows shell is the graphical user interface for the Microsoft Windows operating system. Its readily identifiable elements consist of the desktop, the taskbar, the Start menu, the task switcher and the AutoPlay feature. On some versions of W ...

Windows Explorer File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file ...

. The archive bit's status can also be viewed or changed with the GetFileAttributes, GetFileAttributesEx, and SetFileAttributes Windows APIs. The archive bit can be set or cleared with the attributes property in

VBScript VBScript (''"Microsoft Visual Basic Scripting Edition"'') is an Active Scripting language developed by Microsoft that is modeled on Visual Basic. It allows Microsoft Windows system administrators to generate powerful tools for managing computers w ...

JScript JScript is Microsoft's legacy dialect of the ECMAScript standard that is used in Microsoft's Internet Explorer 11 and older. JScript is implemented as an Active Scripting engine. This means that it can be "plugged in" to OLE Automation applicati ...

. The archive bit is a

and not part of the file itself, so the contents of the file remain unchanged when the status of the archive bit changes.

Alternatives

Relying on the archive bit for backing up files can be unreliable if multiple backup programs are setting and clearing the archive bit on the same volume. Another possibility is to use the

timestamp A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. Timestamps do not have to be based on some absolut ...

of the last change to the file or directory. This is typically the technique used in

UNIX Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

-like operating systems.

References

{{Reflist, 30em Computer archives Computer file systems Metadata

Usage

Alternatives

See also

References