For some time now Advanced Computer Products has had a Sideways RAM cartridge on the market and it has proved an extremely useful addition to my ACORN ELECTRON/ACORN PLUS 3/Acorn Plus 1 system. In fact I didn't think I could manage without it.

But it has now been relegated to the bottom draw of my desk and is no longer used. It's place has been taken by ACP's latest product - ADVANCED BATTERY BACKED BAM (ABBR).

An enhanced version of the original RAM cartridge, it now sports 32k of RAM in two 16k blocks - and is battery backed to boot.

One of the bugbears of ordinary Sideways RAM is that when you switch off the micro you lose everything stored there: The battery in the ABBR cartridge ensures that what you place in the RAM stays there permanently. Well, that's not quite true - it stays there until you overwrite it with something else.

The battery is rechargeable and automatically charges itself up whenever you're using the micro, so it's always in tip top condition.

The cartridge also comes with a set of utilities to enable you to use the RAM as a printer buffer and load, save and create your own roms. These utilities are the same as those found in ACP's Advanced Rom Manager reviewed in the December 1986 issue of Electron User.

ROMLOAD and ROMSAVE load and save ROM images, APB uses one 16k block to extend the Electron's printer buffer, MAKEROM will create a ROM from one or more Basic or machine code programs and LOCK and UNLOCK set the write protect switch - some roms are protected and try to write to themselves, corrupting the code.

A word of warning here: The utilities are stored in the Sideways RAM cartridge and they must be saved before you use it. This isn't made quite clear enough in the accompanying manual and unfortunately if you load a ROM you'll wipe them out. So, save them first.

If you're not sure exactly what you can and can't do with Sideways RAM take a look at the February 1986 issue of Electron User where you'll find a four page feature dealing with this subject.

One of the most common problems experienced by Acorn Plus 1 owners is a lack of cartridge sockets. Many Electron owners have upgraded to discs and have either the Cumana Disk Interface or AP4. These plug into one of the Acorn Plus 1's cartridge sockets leaving only one free.

This makes it very awkward if you regularly use two cartridges, say View and Viewsheet. To go from one to the other you have to to switch off the Electron, unplug one cartridge, plug the other in and switch back on.

However, there is a way round the problem. You can plug in a cartridge, store the ROM on disc using a utility and then unplug it. Now if you load the ROM image into Sideways RAM the Electron thinks you've plugged the cartridge back in.

ABBR contains 32k of RAM and you can load one ROM into the first 16k block of RAM and another into the second 16k. The Electron will think that you've got three cartridge slots-two in one.

What is more, the battery ensures that the information you store there stays put when you switch off, so it's like having two cartridges permanently plugged into one socket.

I must emphasize that the RAM is not part of the main memory map and can't be used for programs. It occupies the same address space as a rom, that is, &8000 to &BFFF and can only be used as a ROM, printer buffer or RAM disc.

Machine code programmers will find many uses for Sideways RAM as it is easily accessed from machine code. You can use it to store data used by programs, text for word processors, utilities and graphics screens.

Sideways RAM is essential for writing your own ROM software and it's not as difficult as you might think. To give an example of what can be achieved with just a few lines of code take a look at the listing accompanying this review.

Run this program to create and store a ROM image on disc. Now load it into Sideways RAM with ASR or ROMLOAD (two utilities provided by ACP with their RAM cartridges) and a !BOOT ROM is created.

Now whenever you switch on your Electron the disc drive will start up and wait for you to insert a disc. Place one in the drive and your micro will automatically *EXEC the !BOOT file.

This file can be used to configure the Electron, setting the colours, keyboard repeat rate, mode and so on, CHAIN a menu, load a ROM into Sideways RAM or simply run your favourite game - it's up to you.

You may find when writing your own ROM software that your micro will lock up if you make an error or typing slip in the machine code. Since the RAM is battery backed it isn't wiped when you switch off your Electron, so the micro will lock up every time you switch on.

However, the solution is quite simple: Switch off, unplug the cartridge, switch on and plug it back in with the power on. This won't damage it, but the contents of the RAM will be ignored by the Electron. Now you can correct the error by overwriting the contents.

Finally, an added bonus is that you can use the cartridge in a BBC Master, so if you have friends with Masters or if you intend upgrading at any time simply unplug the cartridge from your Electron and plug it into the Master.

The contents of the RAM will be preserved thanks to the battery.

To sum up then: It's a superb add-on and an absolute must for all serious Electron users. There's only one thing better than Sideways RAM - and that's battery backed Sideways RAM!

Roland Waddilove