Some file systems distinguish between upper- and lowercase letters, whereas others do not. UNIX falls in the first category, while the old MS-DOS falls in the other. Windows 95 and Windows 98 both used the MS-DOS file system, called FAT-16. Windows 98 introduced some extensions to FAT-16, leading to FAT-32, but these two are quite similar. The following sieries of Windows all support both FAT file systems which are really obsolete now.