What is an Archive File?

Definition of an Archive File

Image of files transferring from one folder to another
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What is an Archive File?

An archive file is any file with the "archive" file attribute turned on. Having a file with the archive attribute turned on simply means the file has been flagged as needing to be backed up, or archived.

Most of the files we encounter in normal computer use will likely have the archive attribute turned on, like the image you downloaded from you digital camera, the PDF file you just downloaded...

run-of-the-mill files like that.

How is an Archive File Created?

When someone says an archive file has been created, it doesn't mean that the contents of the file were changed, or that the file was converted into some kind of different format called archive.

What this means instead is that the archive attribute is turned on when a file is created or modified, which usually happens automatically by the program that creates or changes the file. This also means moving a file from one folder to another will turn the archive attribute on because the file has essentially been created in the new folder.

Opening or viewing a file without the archive attribute on will not turn it on or "make" it an archive file.

When the archive attribute has been set, its value is marked as a zero (0) to indicate that it has already been backed up. A value of one (1) means the file has been modified since the last backup, and therefore still needs to be backed up.

An archive file can also be set manually to tell a backup program that the file should, or shouldn't, be backed up. Modifying the archive attribute can be done through the command line as well as via the file's properties window.

What is an Archive File Used For?

A backup software program, or the software tool your online backup service has you install on your computer, can use a few different methods to help determine if a file should be backed up, such as looking at the date at which it was created or modified.

Another way is looking at the archive attribute to understand which files were changed since the last backup. This determines which files should be backed up again to store a fresh copy, as well as which files were not changed and should not be backed up.

Once a backup program or service performs a full backup on every file in a folder, going forward it saves time and bandwidth to do incremental backups or differential backups so you're never backing up data that's already backed up.

Because the archive attribute is applied when a file has changed, the backup software can simply back up all the files with the attribute turned on - in other words, only the files you need backed up, which are the ones that you've changed or updated.

Then, once those have been backed up, whatever software that's doing the backup will clear the attribute. Once cleared, it's enabled again when the file has been modified, which causes the backup software to back it up again. This continues over and over to ensure that your modified files are always being backed up.

Note: Some programs may modify a file but never turn on the archive bit. This means that using a backup program that relies solely on reading the archive attribute status may not be 100% accurate at backing up modified files. Luckily, most backup tools don't only rely on this indication.

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