I think I read somewhere that there's a limit of something like 250 files per folder, but I believe that was in regard to an older model, so I don't know if that's also true of the PSR-E463. You can store files in different folders, so even if the 250 file limit applies to the PSR-E463, you should still be able to fit more files on a drive by using multiple folders. The thing to do would be store some files on a drive to experiment and see, maybe naming them something easy to track, such as SONG001 through SONG299, so you can see which ones don't show up when you're browsing the drive for songs.