To answer your question would be difficult because you failed to provide the very basic info we require to make a support request, so rather then posting solutions for every possible windows version and bitcomet version and user account controls you may have enabled, why don’t you tell us what your using so we can help you.
BitComet’s downloads are stored in the default download location. That is specified in the program’s options.
Look at those. It will repay you to spend some time exploring them on your own.
Right now, look at the “Directories” branch. Select it and you’ll see where files are currently stored unless you choose to store them somewhere else. So there’s this default location,(which you can set to wherever you’d like), but you can change the storage location for each individual torrent, if you want to. It’s easier to just download them all here, then move them to other locations after they’re downloaded, but you can do it either way.
When you say, “on disk”, it gets very confusing, because it’s ALL on your disk drives somewhere or other. (Even your desktop is stored on your disk, in a folder named “Desktop”).