80-Bus News


January–March 1982, Volume 1, Issue 1

Page 35 of 55


DISKS on a NASCOM by Bob Gilchrist

Most micro users would agree that disk storage, whether minifloppy (5.25") or floppy (8), is an attractive if expensive proposition. In this article I. am going to tackle some of the pros and cons of going to disks, with specific reference to my own experience with the Nascom II. It will end with a description of the system I eventually chose.

The advantages of disks I think are well enough known, but without labouring the point, the chief gain is in speed of access to programs and/or data. In many cases, this makes the machine capable of far more useful work. One only has to edit a few 28K byte articles on a cassette based system to begin to realise the limitations of that method of storage. Cassette files, particularly on the Nascom, are also difficult to keep track of. There is no index or directory to tell you what is on a particular tape, and most people have had to resort to manual methods of book keeping. A tape counter helps, but you very soon find yourself with an awful lot of tapes, cluttered up with things that you’1l rarely use but which would take an age to sort out. A well known law also states that in the process of tidying up tapes you will delete the only copy of your most precious creation. You know the story. ;

So what are the choices for the Nascom II owner? At present there are three disk systems available for the Nascom, which, to avoid confusion, 1’11 refer to as the Henelec, Gemini and Nascom systems in order of their release.

First, the Henelec. This has been around the longest and is a really cheap system consisting of a small pcb which connects to the on-board PIO socket and then to the drives. The controller chip is the Western Digital WD1771, which has been around for some years now. One to three drives can be used. The software is written to support the Pertec FD250 drives, but minor alterations to the parameter table at the start of the FDC EPROM allows almost any Shugart compatible 5.25" single or double sided drive to be supported. The Pertec FD250s are 5.25" drives and they are double sided (there are recording heads on both sides of the disk). In common with most single/double density drives they have 35 tracks recorded at a density of 48 tracks to the inch. Using the Pertec drives with the Henelec system gives a formatted disk capacity of about 160K per drive. The Pertec drives are capable of storing data in single or double density, a possible advantage if future upgrading is a consideration. Obviously, double density stores twice as much as single density. However, due to the simplicity of the Henelec hardware only single density operation is possible. The board can be purchased as a kit (with the FDC software) and the drives can be obtained without a case or PSU (power supply). With a certain amount of ‘do it your self’, a second hand drive, and D-DOS, you could provide a disk system for quite a bit less than 200.00. This is the cheapest route to disks. Gemini also sell this system, packaged in.a nice case with the PSU, and known as the G805, costing about 395.00 + VAT, if you can afford it.

Four alternative operating systems are available for the Henelec: D-DOS, (“DOS’ stands for Disk Operating System) a very simple system rather like using a cassette tape, (you still have to note where everything went) this is very cheap but a little tedious to use. DCS-DOS is a lot more elaborate and overcomes all the disadvantages of D-DOS – where a dedicated Nascom DOS is required DCS-DOS has a lot going for it. POLYDOS 1 is in many ways similar to DCS-DOS (but costs more). It has by far the best documentation of any DOS yet seen (even the professional ones) and has many nice enhancements over DCS-DOS. All three DOS’es leave the Nascom memory map alone and in most cases all existing Nascom software will run. Lastly there is CP/M 1.4 and latterly CP/M 2.2, costing about the same as POLYDOS. This changes the

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Page 35 of 55