The Henelec disk system was originally designed for the Nascom computers. It was supplied as a kit, with one or two drives storing 80k (SS) or 160k (DS) each. It had an internal power supply (G804) and control board using the WD1771 controller with no external data/synch separator (it was discovered, after a hard struggle in trying to get one to work, that it actually worked well without one!) and was supplied a box containing either one or two single density (G805-1 or G805-2). It connected via the PIO rather than the bus so it wasn’t exactly fast. Up to 3 drives could be used. Single density only, 35 tracks.
The vertical row of six pads and three links at the right hand side of the pcb was for connection of an external data/synch separator should it become necessary.
As this was a Henelec system (produced by Henry’s Radio Ltd.) the operating system was D-DOS (the D is for Dave Hunt, who wrote it!). D-DOS came as two 2708 EPROMs, just 2k long in total. It was basically a “floppy tape recorder” and had four commands: Read, Write, Format and N (return to Nas Sys). Not really a DOS as it was up to the user to keep a record of where everything was stored on the disk!
When this was sold as the G805 drive it was only sold ready-built and tested, with one or two double-sided 160k drives. The software is compatible with both systems.
The following files don’t appear to form a complete D-DOS, even when taken together.
The hardware, though simple, proved to be popular as it only required the presence of a PIO on the system to operate. It was a very good (if slow) introduction to disk systems. Dove Computer Systems later produced DCS-DOS for this hardware.
nascom.info 