If I overwrite a file in Word, it's gone. But when I install a mod and I overwrite files and then uninstall the mod it seems to put the original files back.

How does this work? Backs them up somewhere? Uses versions?

Sorry if it's a dumb question but it's been bugging me for some time.

Depends on which tool you're using for mod management. In the case of OBMM, if another mod uses the same file it won't remove the file, although the installed version will still be the most recent version that was installed. In other words, if you install mod #1, then mod #2 overwrites mod #1's files, and you then uninstall mod #2, the files that mod #1 shares will remain but it will still be the version used by mod #2 as opposed to mod #1 (since you overwrote them).

In the case of BAIN, I believe it works similarly except that BAIN will actually replace the previously overwritten files from the package for mod #1 when you uninstall mod #2.

If youre using obmm to install mods, obmm will reinstall overwritten versions and files when the overwriting file is deleted. All your mod files are contained in the omod, and installed in your data folder so you kind of have 2 copies.

I understand how mods overwrite each other, bu I'm thinking about vanilla textures and meshes. Here is an example.

I use Wrye Bash to install a mega texture replacer. It overwrites hundreds of files in the Textures subdirectories. Where are the vanilla files backed up to?

Tomorrow I uninstall my mega texture replacer and Oblivion is vanilla once again. How?

This answer depends on how you install and activate mods. If you have OBMM, an individual mesh will onverwrite part of a file that is contained in a BSA, but will not erase it at all. if the mesh is just a mesh, like a modded skeleton needed for animations to work, overwriting the mesh will erase it from your Data folder. Using Bain avoids this completely. Older mods that required you to modify the information in a BSA could really ruin a game.

The vanilla files (almost all of them, anyway) are in the BSA files that come with the game (Oblivion - Meshes.bsa, Oblivion - Textures.bsa, etc) - those are archive files similar (in concept) to a .zip except that Oblivion can read them. So the game basically uses a file if there's one in the folder (like your texture overhaul), and if there's not, it goes back to using the BSA. So I think that might be the answer to your question?

Yes that answers it. Thank you.