Bethesda mod archives
The Gamebyro engine can load files from specialised archives into the game on startup. This allows DLCs and mods to package all their files together without worrying about them being accidentally overwritten and further simplifies the modding process by minimising the number of files. These archives can be either BSA (Oblivion, Fallout 3, Fallout New Vegas and Skyrim) or BA2 (Fallout 4 and Fallout 76) format files. Extracting or modifying archives should be considered an advanced modding technique and in most cases is unnecessary to allow the game to function correctly.
Mod archive compatibility
The BSA and BA2 archives are not automatically compatible with all games. Even among the variations of the same file type, they can cause unwanted side effects such as preventing the game from starting up. The table below lists the types of BSA and BA2 and how they behave with each Gamebyro title. The version of the archive can be determined by inspecting the file header.
|Game||BSA v100||BSA v103||BSA v104||BSA v105||BA2 v1|
|Fallout New Vegas||Incompatible||Untested||Compatible||Untested||Ignored|
|Skyrim (2011)||Incompatible||Limited Support||Compatible||Incompatible||Ignored|
|Skyrim Special Edition||Incompatible||Incompatible||Incompatible||Compatible||Ignored|
|Fallout 4 VR||Ignored||Ignored||Ignored||Ignored||Compatible|
Below is a more detailed explanation of each status.
- Untested - This combination has not been tested, feel free to update this article if you are able to test.
- Ignored - The game will not attempt to load this file.
- Compatible - This is the intended archive format for this game and is fully compatible.
- Limited Support - This archive type is not intended to be used with the game but does appear to work. The exact impact on loading times, stability or general performance is unknown. It is not recommended to continue to use this combination.
- Incompatible - This combination will cause a critical error, usually crashing the game.
Mod manager archive checking
Some mod managers include a feature that will automatically check archive versions and identify any mismatches. At the time of writing, only Vortex and Wryebash include this feature.