Archive Bit Attacked in Press

Writing for ComputerWorld, W. Curtis Preston proclaims that "the Windows archive bit is evil". The archive bit is a binary flag associated with every Windows file; it's always equal to either 1 or 0 for a given file. When a file is first created, the archive bit is set to 1. Likewise, any time a file is later modified, the archive bit is set to 1. The only time the archive bit for a given file is set to 0 is if some program specifically tells Windows to reset it.

The basic idea behind the archive bit (which is older than Windows -- it's as old as CP/M, if not older) is that backup software can reset the archive bit to 0 when it backs up a given file. Then, the next time the backup program runs, it could easily locate just the files that were created or modified since the last backup, since those will be the only files whose archive bit is not cleared.

One problem, as Mr. Preston points out, is that there's only one bit, and sometimes more than one piece of software is performing backups on a given Windows machines. In general, you want software that lets you specify how it decides whether or not a given file needs to be backed up. Software that relies completely on the archive bit to serve that purpose might get you into trouble.

See Also

• A bug (KB178414) in which NT 4.0 did not set the archive bit when renaming a file, causing backup programs that relied on the archive bit to potentially fail to back up that renamed file.

March 29, 2005March