It's difficult to say how much memory the average BBC Micro or Electron has these days. People keep producing memory extensions - like Shadow boards and Sideways RAM.

Now Advanced Computer Products (ACP) has managed to squeeze no less than 256K of RAM into a standard cartridge for the Electron and Master 128. The Advanced Quarter Meg RAM, or AQR, provides sixteen Sideways RAM sockets, which can be used for running ROM images or as a silicon disc - or even a combination of both functions.

The company has also enhanced its Advanced 1770 DFS and Advanced Control Panel ROMs for use with the RAM cartridges. The Control Panel can now cycle through the sixteen pages of sideways memory, allowing you to select any ROM images that might be in there.

However, most people are likely to use the 1770 DFS, which has new commands, and is being offered as a package with the AQR. Some of the commands have been extended to make full use of the sixteen banks of memory, and two new commands have appeared. These are *SRACCESS, for write protecting and unprotecting the banks, and *SRACCESS, for write protecting and unprotecting the banks, and *SRPAGE, which is used to select which bank you want to use.

For example, if you have several ROM images stored in separate banks, you can switch between them as needed. The image is automatically initialised, so there's no need to hit CTRL-BREAK as you do when using the Master's *SRLOAD command, although there could be problems with ROM software which needs to claim workspace to work properly.

If you're using the ACP DFS in the Master, you'll need to switch off the Acorn one or you'll get command clashes. Regrettably, this also switches off useful commands like *SRLOAD. Unfortunately, ACP hasn't supplied equivalent commands in its DFS, so you'll need to have another utility ROM with a ROM image loading command, unless you are going to use the AQR just as a RAM disc.

Of course, there is no reason why you shouldn't do that. Indeed, that's how I found myself using it. It makes disc operations very fast. ACP has a demonstration program which loads in consecutive graphics screens, and the result on the Master is smooth animation with no screen flicker. It's only marginally slower when used on the Electron.

The fact that, using the Advanced 1770 DFS, you can configure the RAM disc to be any drive - including drive 0 - is a nice touch. Software which assumes you're working with drive 0 can still be used with the RAM disc.

Any of the AQR's RAM sockets can be used for the silicon disc - they don't necessarily have to be in a single block. That means you can have a variably-sized RAM disc, in steps of 16K, interspersed with ROM images.

The quality of the product is up to ACP's usual high standards. All it needs now is for ACP to provide a battery-backed version of the AQR. It may sound like I'm asking a lot, but the company is probably already working on it.

As it is, the AQR is a very inexpensive way of getting a RAM disc - which is how most people will end up using the cartridge. And with the latest version of the Advanced 1770 DFS, which you'll need for all the more interesting features, it forms a very fast and powerful filing system.

The AQR costs £79.95, or £99 if you buy it with the Advanced 1770 DFS. An inexpensive upgrade is being offered for existing 1770 DFS owners.