In my data folder many files, like textures and meshes, are in .bsa format instead of being simple folders. I have much experience with mods and I found this problem out when I tried to install one. I used to have many patches istalled but I had to change my hard disk since my old one was damages by power, so now I just have oblivion installed.

Sorry, but I'm not sure what point you're trying to make here.

The BSA files are archives of loose files. Vanilla Oblivion stores them that way. Many mods come with BSA files containing their meshes, texture, sound, etc., as that cuts clutter. It has been discussed that the BSA should be the standard for mod files but it is not widely adopted.
When adding mods and patches, you can expect a mix of BSA files and loose files (files that are in data\meshes, data\textures, etc). So this is normal.

Edit: Ah, never mind.

The reason it's not been widely adopted is because the game engine has a hard limit on the number of ESM+ESP+BSA files you can store in Data before it stops working properly. That limit is 400 files, which doesn't sound like a whole lot, but in these days of folks with 200+ mods installed it adds up fast. The ESM/ESP files can't generally be avoided, but the one thing modders can do is pack their files loose instead of in BSAs to prevent or at least delay the point at which people hit this hard limit.

The problem is made worse by the fact that some people get hit with the symptoms with as few as 325 files in the Data folder. That doesn't leave a lot of room for error. Symptoms range from missing textures and meshes to CTDs.

The point I'm trying to make is that something has gone horribly wrong with my installation because I can't do anything with bsa files and I can't install any mods. Instead of having a simple folder named "textures" which I can open and find other folders named "characters" or "weapons", I have a .bsa file named "Oblivion - Textures - Compressed.bsa"..

...which is exactly how it is supposed to be, and absolutely nothing has gone wrong. A bsa file is a compressed archive containing textures/resoureces etc., and Oblivion reads them and treats the content as if they were loose files. If you rather want all the loose files, use OBMM to unpack the BSA files.

Btw, "Oblivion - Textures - Compressed.bsa" is one of the bsa files that came with your Oblivion disc, and has been that way all the time.

Ah thanks, I had no idea. It's just that I don't remember it ever being that way or using OBMM to unpack them. Aren't the loose files compulsory if you want to install mods?

btw I didn't mean to sound rude before, I just didn't know it was supposed to be like that..

You don't need to unpack the bsa files to mod. Oblivion will load loose files and bsa files.
To install your mods just place the mod's textures and meshes folders in your oblivion's data folder then check off the mod's esp file in the oblivion launcher or in Oblivion Mod manager (OBMM).

That's because you don't need to. If by chance you're missing a particular folder, like Textures, all you need to do is create it yourself. But the game will run just fine with only the BSA files and that doesn't prevent you from adding mods to your game.



No. The only thing that's compulsory is the proper folder, like Textures, Meshes etc. You just dump the files for the mod into those in the same format as what the game uses inside the BSA folders. Most mods will have everything sorted for you so it's just a question of copying the various folders and esp file over to your Data folder.

In a clean GOTY vanilla install you only get the Music, Textures, Video, and Shaders folders in the Data directory, with the Textures folder only having the terrainnoise.dds. The Meshes folder gets created with installing the unofficial patches and other mods.