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X-DDOS is a floppy disc and hard disc operating system from the german company [[Dobbertin|Dobbertin Industrie Electronic-Elektronik]]. It was first released in 1988. It provides 0.7 MB floppy disc formats for B drives and allows to access the [[Dobbertin Harddisc]] HD20. X-DDOS is delivered as a 16 KB EPROM with a lot of software and a manual. X-DDOS has the ROM name 'XDDOS ROM' but shows a sign-on message of "X-DDOS 2.10 (C)1990 Dobbertin GmbH"  * X-DDOS can be used as a rom 7 replacement.* X-DDOS can autoboot CPM if it's ROM 0.* X-DDOS has a checksum check == RSX commands == (same operation as [[AMSDOS]]): |A, |B, |CPM, |DISC, |DISC.IN, |DISC.OUT, |TAPE, |TAPE.IN, |TAPE.OUT, |DRIVE, |USER, |ERA, |REN (same operation as [[VDOS]]): |CAS, |CAS.IN, |CAS.OUT, |ATTRIBUT, |FORMAT, |SLOW, |FAST, |ROMOFF, |AMSDOS, |X X-DDOS extras: |SYSCOPY, |TYPE, |GDUMP, |DIR128, |DIR64, |HELP, |XDRIVE X-DDOS 2 extras: |COPY (great command to copy files from any drive/partition/user-number to any drive/partition/user-number. That can be users from 0 to 15 and A, B, C, D, E, F and G where C = RAMdisc and D, E, F, G = Harddisc) |HELP,<number> - display list of RSX commands for the given rom <number> |X,|XDRIVE - swap logical A and B. Normally logical drive A accesses unit 0 and logical drive B accesses unit 1. Therefore using |X:|A will access unit 1 as logical drive A and unit 0 as logical drive B. |CPM or |CPM,<drive> - Boot CPM from drive A, or chosen drive. A=0,B=1,D=3,E=4,F=5,G=6. Can boot from D,E,F,G if HD is detected. Can't boot from drive C. == Booting CPM == The process to boot cpm is the same on floppy discs and hard disk and uses a common read sector function that re-directs to low-level functions based on the chosen drive. Using |CPM,<drive> you can define which drive to boot from.  When |CPM is executed:* on 2.10 and later, the hard disc is detected and be4b is set to ff if detected, 00 if not detected.* the bios jumpblock is copied to be80 from c07b.* iobyte (0003) is set to 81* the current drive is written to &0004. A = 0, B = 1, D=3 etc.* 'enter firmware' (&ad33) jp is setup.* the XDPB is queried to find the location of the boot sector* the boot sector is loaded to &100.* if the boot sector has code, then the boot sector is executed from &100.

X-DDOS supports CP/M and CP/M Plus on 0.7 MB B-drives. The RSX command !HELP displays&nbsp;the command summary of X-DDOS. The commands of AmsDOS are integrated as a subsetand can boot from either disc drive.

Further * XD-DOS 2.0 and 2.10 support the [[Dobbertin Harddisc|HD-20]] hard disc drive. The hard disc  * XD-DOS auto detects if the HD20 consists of is connected. A message "* Harddisc not active *" is displayed if it is not. This is shown below the ROM sign on message. * XD-DOS maps the HD20 to four partitions with 5120 KB each. X-DDOS allows the access to this 5 MB partitions Each partition is accessed by using the logical drive letters D, E, F and G.  * The integration of X-DDOS with the firmware allows to load some games and demos from hard disc. Also  * CP/M and CP/M Plus can be booted from hard disc.