XD-DOS is an expanded disc operating system developped by the german software comany Dobbertin.
XD-DOS was delivered on an 16 KB EPROM, with a lot of software and a manual.
It supported 0.7 MB disc formats on DS, DD disc drives. The XD-DOS also supported the 704 KB Vortex format, which is standard for 80 track drives in germany.
Further XD-DOS 2.0 and 2.10 support the HD-20 hard disc drive with 20 MB disc space, that was divided into four partitions of 5 MB. It is also possible to start CP/M 2.2 or CP/M Plus from the hard disc.
The XD-DOS ROM contains a broad variety of RSX commands. The RSX commad !HELP shows them.