In the States, you can buy almost any sort of hardware or software add-ons you require for your 8-bit Atari, but there has long been a lack of such support in the UK.

Now London-based company Computer Support can fill that gap. XOS is its modified operating system, and forms the basis of many of its products.

It will allow most old 400/800 programs to run correctly on an XL or XE because it basically converts the new OS back into a reasonable facsimile of the older version and uses the extra 4K now available to good effect.

It includes a whole host of extra features such as 820 baud cassette saves and holding the bank select status upon reset.

Most of its features are simply window dressing, but it really comes into its own when linked with other programs - such as the 80 column version and Ultimon.

The 80 column XOS chip allows you to select 80 column mode simply by holding down the Select key on power-up.

The 80 column display is based on a Graphics 8 screen in black and white and is reasonably readable on a cheap monitor. On a TV though, you could end up with eyestrain.

But be warned - the 80 column mode may not work with your particular word processor or database.

Ultimon is another option available with XOS and it provides a permanently resident machine code monitor. This can be called from Basic, or by holding down Select and pressing the Reset key. The display shows you the current status of the processor, plus the contents of the current program counter and a section of memory.

It has the facility to view, disassemble and alter memory, load and save given disc sectors and run programs.

There is no breakpoint facility, but there is a very limited single step mode. This should be very useful to the machine code programmer who wants to check and modify his code before running it.

The 130XE version uses the extra banks to avoid corrupting the main screen display and zero page locations, which is a major failing of the older versions.

You could consider using the Computer Support tripler board to allow you to put both the original OS and two new chips into your machine and switch them in and out as required.

This is very useful when you bear in mind that some games will not run at all with an XOS chip in place.

These chips are of limited appeal to the straightforward games player, but if you are a programming enthusiast they could be right up your street - if a little on the expensive side.