How does steam work?
How does steam work?
It only retrieves the necessary files. Should it be a bug fix, it will replace the files listed in the update, unless there is an issue, in which case existing files remain intact.
The game version installed is identified by Steam as a "manifest." Various language versions of the same game are referred to as "depots," while the complete game is identified by its "appid." When checking for updates, Steam sends your appid, depotid, and manifest version to its servers. It receives feedback indicating whether any new manifests have been released. The manifest details exactly which files have changed between versions, allowing Steam to download only the updated parts when an update is available. You can explore individual changes using steamdb.info, such as the main data file for Fallout 4 and the associated manifests.