Root directory, where is it?

[WeeeBen]

Hi,

Tutorials on how to install a patch talk of installing the folders into the root directory.
There's nothing that says root directory, what's the modern term for root directory?

Inside the 3 folders of the patch, there's only a few files, if I drop them into this root directory, will they just load up the files into the corresponding folders?
the folders seem to have more files and i'm worried dropping in the whole folders of patches will replace the entire folder?

Sorry if I don't make sense.