80-Bus News


May–June 1983 · Volume 2 · Issue 3

Page 52 of 59

Now a request – “What is the best controller to purchase, first for a DOS, and later CP/M – MAPVFC, GM809, GM829, LUCAS LOGIC ?” My biased reply to that is GM829 – why? – it’s the one I use and the only one I know about in any depth. (GM829 has superceded GM809, but you may be able to get 809s that have been traded in for 829s – check with your dealer).

Seriously all I can suggest is that you draw up a list of your current requirements, your future requirements, the capabilities of the boards, and then make a decision. All the boards mentioned meet the basic requirements of: a) They work. b) They are 80-BUS compatible. This just leaves the important facts of price/​facilities/​support to influence your choice. I list below some pointers for your thoughts:

Price: Can you afford it/is it worth it? Bear in mind that by the time you’ve added a DOS, the drive(s) themselves, power supply and connecting cables, a small saving in the price of the controller will become a very small saving in your total outlay. I’m not suggesting that you disregard the price, but in the long term the more important factors are facilities and support (below).

Facilities: What range of drives does it support? (3″/5″/8″/Winchester?). (Note that the new Sony 3″ drive looks to the controller like an 8″ drive in terms of data transfer rates, although the drive connector is different again being a 26- way one.) Will you ever want to use 8″ and 5.25″ drives simultaneously from the same controller? (GM829 offers software selectable drive type). If you are likely to change between 8″ and 5.25″ drives sometime and are happy to change straps, does the board layout allow both drive connectors to be fitted, or do the connector fields overlap?

Support: This is a major factor that isn’t always given the attention it deserves. What disk operating system do you want to use? (NAS-DOS, Polydos, QDOS, CP/M etc). How does this restrict your choice of controller? If you want to use CP/M eventually, whose implementation of CP/M do you want to use? (Your own/​Gemini/​Nascom/​MAP80/​Independent). NOTE quite a lot of the criticism of CP/M that appears in the computing press from time to time should be more rightly directed at the writer of the BIOS rather than Digital Research. A good BIOS with adequate error trapping and various extended features can make a remarkable difference to a user’s view of CP/M. A ‘plain vanilla’ BIOS can leave a lot to be desired.

What hardware do you already own? This is fairly important as for example Gemini’s CP/M systems are based upon Gemini’s disk controller card and the Gemini IVC. There are versions that will run on Nascoms (with and without IVCs), but they provide no support for the Nascom AVC or the MAP low-cost video card. Similarly the Nascom CP/M system is based on the Nascom disk card and won’t support the Gemini IVC. This is the burden you have to bear for owning such a flexible system. The possible hardware permutations are high, and no one software product is likely to support every hardware permutation. Each manufacturer is likely to support his own product(s), and, depending on how he sees the market, may extend his support to include various boards from other manufacturers that may be used in conjunction with his product.

(I gather an optimist rang up Gemini one day to ask if they did an implementation of Digital Research’s CP/M to run on a NAS­COM2 + RAMB + Nascom AVC + Nascom disk card – not a Gemini product in sight!)

Another question in the same letter – “Can a ‘virtual disk’ work under DOS or must I have CP/M (MAP80)?”. I don’t believe any of the DOS’s support virtual disk, but most CP/M implementations do. The Gemini CP/M currently supports any “page-mode’ RAM (e.g. Nascom RAM B, GM802, MAP256k) for virtual disk, and also the forthcoming GM833 RAM-DISK (see below). For full support of a multiple MAP card system you have to go to MAP or use Richard Beal’s SYS. For those who can’t get enough of it Mr R.J.Drew (_ ___________, Armathwaite, Carlisle) has a cut-and-strap method of modifying the MAP RAM cards to provide a total of 4Mbytes for a virtual disk. (This assumes you’ve got the space/​amps/​money available for the 16 boards). With Gemini’s GM833 you can reach a total of 8Mbytes without any cut-and-strap, but you’ll still need the space/​amps/​money for 16 boards.

Page 52 of 59