INMC 80 News

So it worked, what next, we three could all take benefit from the disk system, but surely, we thought, some other people might like it as well. We offered it to Henry’s Radio, for them to produce it as a kit on a royalty basis, so they could have all the agro, whilst we sat pack and collected the money. Alright in theory, but it was still only one prototype and a rats nest at that. Peter had a prototype pcb laid out, and as with these things, whilst the rats nest worked perfectly, the pcb was noisy and unreliable. A lot of work went into getting that pcb reliable. Then I set to, to turn the whole thing into a production job, and write the words. By that time, a lot of other people had got to hear what we were up to. Here were people who might actually pay money (or offer services) to get their hands on a prototype, and we needed services, and prototype testers. In all, six production prototypes were made, and shunted off in different directions, whilst we gaily accepted offers of help in return. Dear old Richard Beal offered to write the CBIOS for a CP/M system, and ended up with an incredibly neat piece of software called SYS. Other offers were to investigate the feasibility of adapting the system to 8″ drives, testing with various software houses’ CP/M software, etc. I decided that a simple ‘floppy tape recorder’ might be a nice idea, and as I always need practice at software I sat down and wrote D-DOS (D for Dave, by the way. Modest aren’t I). Peter decided that ED (part of CP/M) left a lot to be desired, so DISKPEN started to see the light of day.

So it was nearly altogether, Henry’s advertised the kits, nearly all the components for the initial batch of 50 were purchased, and our bit was almost done. Henry’s called the thing the Henelec Disk System, and already a comforting number of orders were in the bag. Then Gemini moved into the scene. “Why not,” they suggested, “Put the whole thing in a box, built, with double sided drives, and sell it through other dealers as well. Disk systems are serious and expensive toys, and not all potential customers want (or can build) kits.”. ‘Sound thinking, Batman’, we’ll do just that. Gemini designed a power supply, to drive two disk drives and the controller card, and an attractive case, made to match the rather stylish Kenilworth Nascom case. The initial production order went up from 50 to 250, and the original launch date was put back two months to allow time for the software to be rewritten for double sided drives and five times the number of pcb cards to be made. The Gemini G805 was born.

It was decided that the Gemini would only be available built and tested, whilst the Henelec would only be availble as a kit. The software is compatible with both, and the Gemini has double sided drives with a total capacity of 160K each whilst the Henelec is available with both single and double sided drives with capacities of 80K or 160K, the single sided system remaining compatible and cheaper.

One of the group members has been fortunate enough to secure one of the first 5 Henelec Disk Systems (it wasn’t, it was a built Gemini, Ed.), and in the short time he has had it, has managed to disassemble both the unit and the software. Over a few pints in a rather plush pub in the wilds of Cheshire we have written this short article for the benefit of anyone contemplating buying the system. The system that we are using consists of a single drive, the disk controller and a D-DOS operating software. We would have liked CP/M as well, but financial constraints prevented this at the time. Having only D-DOS means that this article is limited in that it can not discuss the use of CP/M on a Nascom, however, as CP/M is such an accepted standard, there are plenty of books and articles regarding this. Implementing CP/M on a Nascom 2 appears to be quite straight forward by replacing the MD PROM, but on a Nascom 1, it does require some board modifications so that the memory map can be altered to suit.

The Hardware

The system we have consisted of a single drive made by Pertec, fitted in a case (designed to take two such drives), of two part steel construction. The back plate carries the mains on/off switch, fuse, power regulator transistors, mains lead