What Is an Archive File?

Definition of an Archive File

Image of files transferring from one folder to another
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An archive file is any file with the "archive" file attribute turned on. Having a file with the archive attribute turned on simply means that 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.

Note: Terms like archive, archive file, and file archive are also used to describe the act or result of compressing and storing a collection of files and folders to a single file. There's more on that at the bottom of this page.

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.

How to Manually Change the Archive Attribute

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 with the attrib command. Follow that last link to learn all about how to use the attrib command to view, set, or clear the archive attribute through Command Prompt.

Another way is through the normal graphical interface in Windows. Right-click the file and choose to enter into its Properties. Once there, use the Advanced... button from the General tab to clear or select the box next to File is ready for archiving. When selected, the archive attribute is set for that file.

For folders, find the same Advanced... button but look for the option called Folder is ready for archiving.

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. Fortunately, most backup tools don't only rely on this indication.

What Are File Archives?

A "file archive" might sound identical to an "archive file" but there is a notable difference regardless of how you write the term.

File compression tools (often called file archivers) like 7-Zip and PeaZip are able to compress one or more files and/or folders to a single file with just one file extension. This makes it much easier to store all of that content in one place or to share multiple files with someone.

The top three most common archive file types are ZIPRAR, and 7Z. These and others like ISO, are called file archives or simply archives, regardless of whether the file attribute is set.

It's common for online software downloads and backup programs to archive files to an archive format. Downloads typically come in one of those big three formats and an archive of a disc is often stored in the ISO format. However, backup programs might use their own proprietary format and append a different file extension to the file than the ones just mentioned; others might not even use a suffix at all.