 MS-DOS 3.0 introduced support for high-density 1.2 MiB 5.25-inch diskettes (media descriptor 0xF9), which notably had 15 sectors per track, hence more space for the FATs.FAT12 remains in use on all common floppy disks, including 1.44 MiB and later 2.88 MiB disks (media descriptor byte 0xF0).On August 14, 1984, IBM released the PC AT, which featured a 20 MiB hard disk and PC DOS 3.0.