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(GM829 has superceded GM809, but you may be able to get 809s that have been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
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
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
ecard – 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.