| Microdrive |
John Gilbert talks to Ian Logan, the man who wrote the software for the ROM in the new Sinclair storage device
DR IAN LOGAN leads a quiet life, despite having written several popular books about computers and having just completed work on the Microdrive ROM. There are few journalists pounding at his door and he prefers it that way. He has a country practice in and around Lincoln. He lives on the outskirts of Lincoln, with his wife and children. Apart from the odd journey to the Cambridge offices of Sinclair Research or to London to take part in a Microfair, he handles most of his business by post or on the telephone.
Logan's Spectrums are in the bedroom. He has two of them set up with a dot-matrix printer. Surprisingly that collection occupies only a quarter of the room; the rest of it is not cluttered with the debris of an interest in computers.
The two Spectrums are sufficient to run all the facilities of Interface One and Microdrives, of which he has two. He explains the development and use of the new Sinclair peripherals with the case of a schoolteacher who has spent several years lecturing on a subject.
"I first started to work for Sinclair last December. I went to Cambridge and Nigel Searle asked me if I would like to do some work and I could write a book about it.
"At that time the Microdrive did not exist. It was developed in a large crate with the ULA at the centre. There is very little to the insides of the Microdrive. There is one ULA and the dual heads which read the tape, the Microdrive program was developed on EPROM. If there were corrections to the program I would go to Cambridge with the alterations and we would blow a new EPROM.
"In the end, Martin Brennan, who was in charge of the project, said 'Right, that's the end'. I have no doubt that he had added two extra things by the next morning."
Logan wrote the software for the Microdrive ROM only. It was Brennan who was responsible for the design for the network and he wrote most of the software which drove it as well.
In the early stages Brennan was known as the man who could get everything. He was the one who talked to those above and below. Logan says:
"His importance to the project was shown when you entered the office at Cambridge. One of the places which was off limits was the television laboratory. There were signs saying that it was a restricted area and no-one must enter. When you wanted to see Brennan there were no signs in his part of the office but you had to pass the paper shredder to reach him."
| 'At the moment there are still two definite bytes in the ROM of the device, which Logan hopes will be cleared quickly before the control program is put into the ROM' |
The Microdrive controller program has not been put on to ROM, even though at least 1,000 have been sent to customers. Logan says:
"One reason the Microdrive still contains an EPROM is that Sinclair Research wants to re-design the circuit board at some stage. When you can get a Microdrive with a nicely-covered ULA and tidily-set-out board you will know that Sinclair is finally convinced that everything is right."
At the moment there are still two definite bugs in he ROM of the device, which Logan hopes will be cleared quickly before the Microdrive control program is put into ROM. One of the problems which occurs is that the Spectrum does not select the screen automatically when it returns from working with the Microdrive.
Logan thought of a simple answer to that during the interview. While he was demonstrating the network he found that by selecting the screen every time the computer discontinued work with the Microdrive, the problem would be eliminated.
Logan gives a very interesting description of how the interface devices work. He says: "I like talking to people as, when you are explaining things, you develop new phrases and ways of putting things over."
He described the network as a fantastic piece of work, especially where the software for its operation is concerned. It will enable two Spectrums to be connected so that, for instance, two people on separate Spectrums can play the same game and influence each other's rate of play. He says:
"I think there is a great potential for two-player, interactive games. With the network you will be able to have two people playing a game. Each player will be influenced by the other's actions. You could imagine what it would be like to have something like The Hobbit using the network. You would not only have the computer continuing to perform actions even though the players are not doing anything - the players would also be able to affect what each other found in locations. I would be interested to see what a software house makes of the possibilities."
The RS-232 interface provided another interesting demonstration. Logan explained that it could be used to connect two Spectrums but it would also allow you to put any other piece of equipment on to the Spectrum. He says:
"The possibilities are endless. For instance, you could connect a BBC micro to a Spectrum using the interface. The Spectrum could then be told to wait for a signal and anything which you type on to the BBC keyboard could be printed on to a Sinclair printer attached to the Spectrum. Unfortunately you cannot tell one computer to inform another that you want to talk to it. You have to set the other computer to listen for any signals."
Logan's enthusiasm for the subject shows that he is still learning about the Interface and Microdrive. It seems that even though you help in the development of a device you can still discover new areas to look into weeks after you have finished the project. For instance, it is possible to speed the access time of the Microdrive to some extent if you have two parts to a program which are loaded separately. You may have a screen to load and then the main program. By writing a program to store the first screen, performing one or two CATs and finally saving the second part, the two programs will he loaded in a good position on the tape and will load back reasonably quickly.
If you do not do that the tape loop will go round one extra time and the two parts of the program will he in difficult positions when you need to find them again.
Many of those tips are in a yet-to-be-published book by Logan, The Microdrive Book. It delves into the workings of the Microdrive and how the Interface is used with it. Looking at the proofs there are plenty of illustrations of how programs and data are stored on tape and how to transmit data over the RS232.
| 'Logan is still learning about the Interface and Microdrive' |
Also included is another aspect of the Interface which enables a user to patch, or add, extra Basic commands to the Basic interpreter. It means that you can write machine code extensions to the language and Logan has been busy doing so already.
"You can re-define the original keywords to do different things but you cannot define your own keywords," he says.
Logan has created several new commands. One of them will allow the user to change the colours on the screen without using the CLS command to clear the screen and re-set the colours. Previously that meant clearing the screen, re-displaying anything which was on it and re-setting the new colours. With Logan's new command the machine does all that for you.
The book is due to be released soon and will be published by Melbourne House. It is likely to be the definitive and perhaps the only work on the Microdrive.
The Microdrive and all the work which he put into it may be behind Logan now. He says that Sinclair Research talks about it and the Spectrum in the past tense and that it arises only occasionally in conversation between the company's staff.
They have moved on to new and different projects, of which they talk only in whispers, but Logan is only just beginning to appreciate the potential of his Microdrive. Like the Spectrum ROM and all of the ZX-81 before it, he will be the one who tells the user what the Microdrive is capable of doing.