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/* Technical */
== Technical ==
Dobbertin HD20 is a hard disk that has an interface that appears to implement the SASI protocol (Shugart Associates System Interface) (a precursor to the SCSI) but which has registers which look similar to those of the OMTI 5510. (The SASI protocol is also used by the SA1000). The controller is a Seagate ST-11M.
(The SASI protocol is also used by the SA1000). The controller is a Seagate ST-11M. There is an expansion port interface which connects to the CPC. It contains a 16KB ROM containing XD-DOS which is normally in slot 6 but can be configured between 1 and 7.
There is a CPC interface which connects to a PC-XT interface.
The OMTI 5510 appears to be very close in terms of operation and commands, but the Dobbertin is probably not this. The command descriptions and operation appear to be the same although the software seems to only use TEST READY, READ, WRITE, SEEK (parking), SET PARAMETERS and FORMAT. Uses [[XD-DOS]] v2.10 (which supports the harddisc, and additionally supports external double sided 80 track disc drives). The 20 MB harddisc is split into four partitions, with drive names D, E, F, and G (drive name C isn't used here, but may be used as RAM disc, in combination with Dobbertin RAM expansion). Under [[FutureOS]] the four partitions are named I, J, K and L. The hard disc is controlled by this I/O Ports:
#FBE0 Dobbertin Harddisc Data Port (read/write)
#FBE1 Dobbertin Harddisc Status (read), Reset (write)
(Exact port decodings to be confirmed; the GALs probably describe it)
The hard drive interface is an PC-XT compatible hard disc interface. The CPC's port mappings are close to the PC-XT's port mappings.
The CPC's port mappings are close to the PC-XT's port mappings. To format the hard disk you need to use the CPM based system tools. To use the tools you need to patch a CPM+ disc so that it recognises the hard disk.
* CPM/AMSDOS format
* 614 cylinders (maybe configured by X-DDOS)
TFM's comment: For FutureOS I researched this hard-disc and I found 17 sectors of 512 bytes per track. It has four heads and 615 cylinders. For optimum speed the sectors and tracks have to be read / written in a defined sequence to reach maximum data transfer speed (about 80 kb/sec). It's not the case that number of sectors, heads, tracks etc. can be redefined (neither software, nor jumpers). These are real hardware values!
== Other harddisc solutions for the CPC ==
