Any file with the "archive" attribute turned on is an archive file. This means that it was marked as something that needs to be saved or archived.
Most of the files we deal with regularly, like the picture you downloaded from your digital camera or the PDF file you just downloaded, will have the archive feature turned on.
How do you make an archive file?
When someone says that an archive file was made, it doesn't mean that the file's contents were changed or that it was changed into a format called "archive."
The archive attribute is turned on when a file is made or changed. This is usually done automatically by the program that creates or changes the file. This also means that if you move a file from one folder to another, the archive attribute will turn on because the file is now in a new place.
If you open or look at a file without the archive attribute turned on, it won't turn on or "become" an archive file.
When the archive attribute is set, its value is marked as 0 to show that it has already been backed up. If the value is one (1), the file has changed since the last backup, so it still needs to be backed up.
How to Change the Attribute of an Archive by Hand
A backup program can also be told manually whether or not an archive file should be backed up.
The attrib command can change the archive attribute on the command line. Follow that latest link to find out how to use the attrib command in Command Prompt to view, set, or remove the archive attribute.
The standard graphical interface in Windows is another way. Right-click on the file and choose "Properties" to get into the file's settings. Once there, use the General tab's Advanced button to clear or check the box next to "File is ready to be archived." When this box is checked, the archive attribute for that file is set.
Find the same Advanced button, but this time look for the option "Folder is ready to be archived."
What's the point of an archive file?
A backup software program or the software tool that your online backup service makes you install on your computer can use in a few different ways to determine if a file needs to be backed up. For example, it can look at the date it was created or changed to see if it needs to be backed up.
Another way to find out which files have changed since the last backup is to look at the archive attribute. This shows which files have changed and need to be backed up again and which files haven't changed and don't need to be backed up.
Once a backup program or service does a full backup of every file in a folder, it saves time and space to do incremental or differential backups in the future so that you never back up data that has already been backed up.
Because the archive attribute is set when a file is changed, the backup software can back up all the files with the feature turned on. In other words, it will only back up the files you need to back up, which are the ones you've changed or updated.
Then, once those have been backed up, the software that did the backup will clear the attribute. Once it has been turned off, it turns back on when the file is changed, making the backup software back it up again. This repeatedly happens to ensure that any changes you make to your files are always backed up.
What are archived files?
Even though a "file archive" and an "archive file" may sound the same, there is a big difference between the two.
File archivers, like 7-Zip and PeaZip, can compress one or more files and folders into a single file with only one file extension. This builds it much easier to keep all that content in one place or share multiple files with someone.
ZIP, RAR, and 7Z are the three most common types of archived files. Whether the file attribute is set or not, these and other files like ISO are called file archives or just archives.
Files are often saved in an archive format by online software downloads and backup programs. Most downloads come in one of these three large formats, and ISO is often used to store an archive of a disc. But backup programs might use their format and give the file a different file extension than the ones listed above. Some might not even use a suffix at all.