I have been using the Kempston disc drive interface on one of my TS 2068’s since early October and I am extremely pleased with the results so far. The Kempston disc interface is intended for use on the Spectrum, In order to use it on a TS 2068, one needs to use a Spectrum BUS adaptor. I’ve been using the one made by Doug Dewey for use with the Spectrum Microdrives.
The disc interface is currently available in the US from English Micro Connection for $119.95, or with a BUS adaptor to fit a TS 2068, $129.95. I have found that the disc interface will not operate with an Emulator, and therefore a Spectrum ROM or ROMswitch is required for your TS 2068. With the disc interface attached, the TS 2068 hangs up in the 2068 mode if you try using an emulator.
The Kempston disc operating system, known as KDOS, is ROM based and eliminates the need to boot from a system disc. I’m told that when the disc interface is used on a Spectrum, the KDOS system message comes up when the Spectrum is turned on. When using a TS 2068, it is necessary to press the interface reset button after powering up before the KDOS system message will appear.
The interface is housed in a small black housing which is simply the standard Kempston joystick interface housing designed to match the styling of the Spectrum +. The interface is designed to lie flat, unlike the earlier Kempston interface box which was vertical in design. The disadvantage of this is that when the disc interface is attached to the back of the Spectrum BUS adaptor board, it adds considerably to the depth of the TS 2068.
Also, the interface does not have a feed through connector. Therefore, something like a Currah u-slot or a Kempston three-way connector is required if you want to add a printer interface as well. I solved this problem by glueing an additional edge connector to the side of Doug Dewey’s adaptor board and wired it up to the existing edge connector on the board. I’ve found the disc interface compatible with both Tasman and Kempston centronics interfaces. On top of the disc interface is a power on indicating LED and a reset button. The reset button is useful for clearing a program without the need to switch off the computer.
With the disc interface attached, the large heat sink on the Spectrum adaptor board gets very hot. However, I have run the system for several hours at a time with no problems and the TS 2068 power supply stays comfortably cool. I think there could be problems using Spectrum BUS adaptors other than Doug Dewey’s EMU-4 which do not have such a large heat sink as his adaptor board does.
I am using the interface with a 5.25 inch single sided double density disc drive which gives me 200K of storage per disc. The Kempston interface is capable of supporting any standard single or double sided double density disc drives in 3, 3.5, or 5.25 inch sizes. I chose 5.25″ discs rather than smaller sizes because of their low price and easy availability. 5.25 inch discs are advertised as low as 50 cents each, although this usually requires the purchase of 50 or 100 discs at a time. I was content with purchasing a box of 10 generic discs for $14 at my local computer store. Also, 5.25 inch disc drives are easy to obtain and even brand new drives with case and power supply can be obtained for as little as $125. My drive is half height and takes up very little table top space.
Up to four disc drives can be supported at one time. I borrowed a friend’s disc drive and power supply which he pulled from his IBM XT. This second drive worked just as well as the one I purchased.
I like the KDOS operating system because disc commands are standard Sinclair syntax preceded by a PRINT#4 command. Thus to load or save a file called ‘TONY’, you would use PRINT#4: LOAD “TONY” and PRINT#4 : SAVE “TONY”. I find this syntax easier to use than that employed by the Sinclair Microdrives. If more than one disc drive is being used, the drive number must also be specified (if it is not specified, then the last drive accessed is assumed by default). In formatting discs, the drive number 1s always required. The command PRINT#4: CAT: PRINT 2 will CATalogue the contents of the disc on drive two.
Two utilities are provided to help transfer files from tape to disc. PRINT#4: COPY will copy files one at a time from tape to disc and if necessary, add headers to headerless files. This routine does not change the syntax of tape files and therefore this has to be done to make programs run on disc. The copy routine cannot handle recent Spectrum software with hyperloaders and problems arise with long programs and those with non-relocatable machine code in REM statements because the KDOS system takes up some system memory (about 800 bytes).
The other useful routine is PRINT#4: CLEAR 0 which replaces all numerical values in a BASIC program by VAL statements thus saving a few bytes each time. This is useful in fitting a BASIC program into the reduced memory space available.
All these instructions are adequately explained in a rather small size instruction book which I had to copy in an enlarged format in order to read easily with my eyesight.
I have found Interface III useful in transferring commercial software to disc. My technique is to make a tape copy of the software using Interface III. This results in a tape version with a simple two line loader. It is then only necessary to change the syntax of this basic loader to KDOS syntax and then about 50% of the time a working disc version results. I modified Tasword 2 basing my modification on a version for the Timex disc drives given by the L.I.S.T. user group.
Why did I choose the Kempston disc system for my TS 2068? There are several reasons and perhaps a better starting point is why choose a disc system at all? My reason came from my experience using Spectrum Microdrives. I have two TS 2068s and using Microdrives on one of them soon put me completely off cassette tapes. I was completely won over by the ease and convenience of fast file finding and loading. I soon got tired of using tapes on my other TS 2068 (as did my children!) and decided to add a disc system to it.
Any disc system I purchased had to work on the TS 2068 in Spectrum mode since most of my software is Spectrum and I want to have access to the 5000+ items of Spectrum software compared with the less than 200 TS 2068 items, much of which is now outmoded. So since at the moment there are no disc systems switchable between Spectrum and 2068 modes, I had to go for a disc system designed for the Spectrum. Next it had to work on an adapted 2068. Not all disc systems designed for the Spectrun will do this. Finally, for reasons already discussed, I wanted to use 5.25 Inch discs. These considerations led me to the Kempston disc interface and two further considerations confirmed that choice. First, price: I was able to put together my system for $220 complete with a new dise drive. Secondly, future support of the system: Kempston seems to be one of the longer lasting and hopefully more stable suppliers of Spectrum hardware add ons. These considerations of mine will not apply to everybody, but I do think the Kempston disc interface should be seriously considered by anyone who wants to add nass storage to their 2068.