It's now possible to have 4Mb of RAM added to your Spectrum. But you'll have to be a wizard with a soldering iron to install the XK expansion, says John Lettice

It may come as a surprise to you, but it's now perfectly feasible to have 4Mb of RAM fitted and working on a Spectrum. This would probably have come as a shock to Stephen Adams, who is responsible for the hardware that's made it possible, when he soldered his first ZX81 RAMpack years ago. We've all grown a bit since then, and the Spectrum is no exception.

The XK expansion system is a simple idea - or to be more precise, it's two simple ideas. And the beauty of it is that the entry level modification costs only £15.95 for, if you're lucky, an extra 16K of memory. "If you're lucky" because some Spectrums aren't 48K at all - they're 64K, and this is a consequence of an early piece of cost-cutting on Sinclair's part.

But the failure rate of 64K chips has dropped recently, so you may find you have extra memory you can't use. The XK is intended to give you access to this, and to RAM up to 4Mb in banks of 32K.

Stephen Adams says fitting the modification is dead easy. I reckon it would be a nightmare. Look at the picture and judge for yourself, but if you're not much cop at soldering, it'd make much more sense to pay the extra to have Television Services do it for you. Once the system's installed, you still have a normal Spectrum, so there shouldn't be any problem loading commerical software. The clever bit, actually getting the XK working, is dealt with by the software.

This has been written for the system by Andrew Pennell, and is called XP Basic - calling it a Basic may be a little overblown at the moment, but the idea was to get a working system out now, and develop the Operating System later.

The extended Basic adds a number of functions, but the system's core is its ability to handle extra pages of memory. These are basically 32K banks of RAM that can be switched in and on, and that can run separate programs, i.e. multi-task, through interrupts.

Think of it this way. Say you want to run a program that ordinarily wouldn't fit in a Spectrum. You can divide it up into subroutines placed on different pages of your expanded memory, and instead of using GOSUB, you'd RANDOMIZE USR 26003:PRINT XXX, where XXX is the page number. The program on that page is executed, then you return to the main program. Multi-tasking is controlled simply by chaining the pages to be multi-tasked together in command line.

But wait, you say, if the pages are operating independently how can you update the value of parameters on a page when they may be changed by another page? This is allowed for. The area of RAM from 2900 to 32000 is for transferring data between programs, and it can be used simply by poking the value into this area then peeking it when you need it.

Windowing is the other major feature of the new operating system. These scroll automatically, without asking you the Spectrum owner's favourite silly question, 'scroll?' Obviously windows are important if you're going to be using a multi-tasking system, and these are perfectly usable, although limited. If you move a window over another, the data won't be refreshed when you take it away - but more expensive machines than the Spectrum lack this facility!

The multi-tasking also has the odd rough edge, most notably the way that, when one of your programs finishes, the others all suspend operation as well. This is fairly easy to deal with, however, and considering the system's low price you'd expect the odd cost-cutting fudge.

True, the commands are a little unwieldy, but if you have Interface 1 you have the option to use shortened commands prefixed by '*'. As far as software is concerned, initially the system looks like being catered for by the small but thriving Spectrum business software houses. Andrew Pennell is looking at modifications of Tasword 2 (4Mb RAM disk? All this could be yours!) and generally the business programs with a modifiable Basic attached shouldn't present too many problems.

To use the system to best advantage, of course, you'll need RAMpacks. These come in 64K batches, and are a bit pricey at £100. If the system takes off, the RAMpack price may come down a little, but think of it this way - for £250 you can get a Spectrum with more user-memory than the QL.

I'm not going to start complaining about anything useful that costs only £20. The XK is a neat little system with great potential. With such a low price you don't have to find excuses for buying. That said, if a bit of word could bring considerable rewards and it if takes off sufficiently we should be seeing enhanced versions. Television Services was a bit cagey about my suggestion that they give me a custom-built 4Mb Rampack though...

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