DISC INTERFACE TAKES THE WAITING OUT OF WANTING
OWNERS of the Spectrum who want a fast method of data storage have, until recently, had to wait for the chance to buy the elusive Microdrive. Technology Research Ltd, however, has now taken the waiting out of wanting by announcing the latest version of its floppy disc interface.
It will accept up to two 5.25in. drives in either 40- or 80-track, single- or double-sided format and is complete with a utility disc.
The interface is in the inevitable black box which fits into the user port at the back of the computer and has a through port for other add-ons. A socket on one side takes the cable to the disc and in the back left-hand corner is a socket for the Spectrum power supply. Unusually the box lies flat and out from the computer rather than standing up; that presumably is to aid stability but if, as is the case with this reviewer, your Spectrum is housed in a full-size keyboard, you could find that the interface ends up being about 1.5cm. off the desk. An empty matchbox placed under the back edge of the interface solves the problem.
Inside the box are two PCBs; the lower one takes the signals across the board to the extension at the back and also houses the power socket and associated chips. The other contains the majority of the electronics, the disc operating chip - a 1771 - a 4K EPROM and the socket to the disc. The socket is suitably buffered so that the disc lead can be removed without crashing the system, a useful feature for BBC computer owners as it is wired to the same standard.
On power-up, the interface loads the contents of the EPROM into the upper 4K of memory and resets RAMTOP to below that. In the version for the 16K Spectrum the program, or more accurately the disc operating system, remains in the interface, but otherwise the two versions operate in much the same manner.
There is a complete range of commands which all have to be typed-in in full; you cannot use Sinclair keywords. The DOS gives a temporary C cursor automatically and will not recognise lower-case commands as it differentiates between the two.
SAVE will save either Basic or machine code but not variables. If the program name is preceded by a $ sign a Basic program is saved; when loaded back it will RUN from line 1. For machine code the name must be followed by three hex numbers which denote the start, finish and autostart addresses of the code.
The only time the system was made to crash was when trying to save a Basic program with the $ sign omitted; all other errors were trapped successfully by the system.
Two levels of protection exist for the user. First there password, which is on the disc. After a new disc has been formatted, using the program on the utility disc, the directory must be initialised using the UNIT command. The disc will then take the name of the current password. That name cannot be changed without erasing the disc.
Second, every interface contains its own code number, and while initialising or later using the LOCK command it is possible, if required, to store it on the disc so that only the interfaces used to save a program can load it back.
The interface proved to be very easy to use and also reliable, apart from the instance mentioned. Almost any Basic program can be saved; only machine code programs which use the upper 4K of memory present - a problem and they are fairly rare. Business software is being written to use the interface.
Priced at £85, the interface is rather expensive but it allows the use of disc drives which are not dedicated to one machine. Also if used with an 80-track double-sided drive it can give 390K per disc at less than £2 a time.
Further information from Technology Research Ltd, 356 Westmount Road, London SE9 1NW. Tel: 01-856 8408.