INMC 80 News

  

October–December 1981, Issue 5











Page 34 of 71











Disk Review

REVIEW OF GEMINI DOUBLE DENSITY DISK SYSTEM

By Ian Henderson

I had been considering taking the road to disks for a considerable time but had been prevented from doing so by one very small fact – there were none available for the Nascom !! Nascom’s own had been promised for some time, but receivership seemed to have well and truly put a stop to that. Then the Comp unit came out and I went to inspect it. There are few words to describe either the hardware or software, all of them unprintable.

Next came the Henelec (meaning ‘of Henrys’) FDC card, and the Gemini G805 disk system that used that card. I went and had a good look at one that a friend had bought and was duly impressed. Unfortunately, by that time, I had read too many adverts and had decided that I MUST have a double density system. There were noises emanating from the Nascom camp again and I decided to wait for ‘the real one’. And wait I did !!

Then, a couple of months ago, INMC80 issue 4 arrived announcing the imminent arrival of the new Gemini double density card. “I’ll believe that when I see it” I said. (Have you noticed the tendency for computers to make you start talking to yourself?) So I phoned my distributor and said “Let me know when you get the Gemini disks”, “I’ve got them”, “No, not the G805 – the new one”, “That’s what I mean”, “*&S*+#$ ... Don’t sell them, I’m coming”. And so off I went and bought myself a G809, a G815/2 and a G513. If that means nothing to you then read on (it doesn’t mean an awful lot to me either so don’t worry).

Gemini G809

The G809 is the disk controller card. It is a standard 8x8 80-BUS (ie Nasbus compatible) card and it comes built and tested. It handles 5.25" or 8" drives of single or double density, single or double sided, 48 or 96 track per inch types. (Note, the 50 way connector for 8" drives {s not supplied.) Up to four drives can be controlled, and all drives are deselected (thus unloading the heads) after several seconds with no access. According to the manual it has ‘variable write precompensation and phase locked loop data recovery circuitry’, or more to the point – it works! As delivered it is set up for Pertec FD250 type double sided, double density, 48tpi drives (350K per drive!). Installation is simple – plug it into the Nasbus, switch the Nascom 2 I/O switch to ‘External’ and go and get a well earned cup of tea!

Gemini G815

The G815 is the disk drive box. This is the same box as that used for the G805 system. It contains either one or two (G815/1 or G815/2) Pertec FD250 drives, and the power supply necessary to power them. On the front an led indicates that the unit is on or off, and on the rear is the mains switch and fuse holder. The unit is fairly attractive and the lid is made of the same plastic coated steel used for the Kenilworth case. With the G815 longside my Kenilworth the whole system (with my APF monitor and Epson printer) looks quite attractive, or to put it another way, the wife no longer objects!! Installation is again simple – plug the 34 way cable that comes out of the back of the drive unit into the disk card (making sure you get it the right way round), add a mains plug, and plug it in. Now go and get another cuppa!

Gemini G513

So now you have your controller card and drive unit, what next? Oh yes, software! The G513 is a “CP/M 2.2 Package for Nascom based systems.” First of all the memory map of your Nascom needs altering to conform to the requirements of CP/M. For N2 owners a new MD PROM (N2MDCPM) is supplied, N1 owners just follow their own instructions. (By the way, for those not wanting to go to CP/M a mysterious item called Polydos 2 is supposed to be available soon.)


This is an OCR’d version of the scanned page and likely contains recognition errors.











Page 34 of 71