Scor­pio News

who were using us as suppliers and technical support. The decision was therefore made to go back to our roots and concentrate only on this part of the computer market.

New premises were found in Wetherby and, as the name Leeds Computer Centre would then have been geographically inaccurate, a new one was needed. I have constantly suffered by living in the North and having a vast number of business contacts in the South, the MD of Gemini being one of the worst offenders. You know the sort of thing where anything north of Watford is in ‘the frozen Worth’, so what better name than Arctic Computers?

Things have gone very well since the move over two years ago. We are just about to branch out and expand the computer graphics side of the company in order to promote PLUTO graphic products on a much larger scale. One of the main areas will be a self drive bureau where time can be bought on our systems in order for potential purchasers to evaluate the equipment on a real project. We will be equipped with facilities for full colour frame grabbing from any source, colour printing, 35mm slide production, A0 pen plotting, CAD, PCB-CAD, Graphics design 2D & 3D, video productions to high band Umatic etc. Purchasers of systems will have access to our wore expensive peripheral equipment at very reasonable prices.

I hope these ramblings serve to explain the company roots and all that remains is to thank all those who have supported us over the years.

B. S. Wingfield, MD, Arctic Computers Ltd.

Technical Query

SYS questions

Could somebody please answer a couple of questions involving the disk routines in SYS18?

1. Why are Shugart SA200 drives only allowed 64 directory entries?
2. Why is ‘side nibbling’ allowed only under Gemini DD format with PERTEC drives? I’m using a Mitsubishi drive and a Pertec drive and it works just well on the Mitsubishi as the Pertec. Also why didn’t Gemini keep the above format for 96tpi drives?

Yours, P Smeesters, Forest Hill, London

Richard Beal, Author of SYS replies

1. I seem to remember that the Shugart SA200 was an 8″ drive. In that case the reason for the 64 directory entries is because that was the original 8″ CP/M disk format standard. In fact 64 is quite a sensible number entries for a disk capacity of about 250K.
2. I assume ‘side nibbling’ means putting data on both sides before moving on to the next track. This improves performance. The reason it was used for the Gemini DD/DS 48tpi format and not for the later 96tpi (80 track) formats is that the first Gemini double density 48tpi format was double sided, whereas the first Gemini 96tpi format weed single sided drives. Naturally Gemini decided to use a format which would allow both single and double sided drives to be used, with single sided disks being immediately readable on the later double sided drives. In fact this required the additional forward thinking precaution of using 4K allocation blocks.
   
   The question of using Mitsubishi drives instead of Pertec appears to relate to the use of ‘Pertec’ in early documentation – probably before alternate suppliers existed. It will work just as well on compatible units