One company which has been giving a great deal of support to Electron owners over the past twelve months has released what could be its best product to date, the Advanced Plus 4 - a disc interface for £80.44.

The AP4 from Advanced Computer Products requires that you have a Plus 1 fitted to your Electron and a suitable disc drive to plug into it. Once installed in either of the expansion unit's cartridge slots, the disc drive is plugged into the port at the back of the AP4 and that's it - just switch on and go.

The heart of the AP4 is the 1770 disc controller chip, which is the same as that used on the BBC B+ and Master series. PAGE remains at &E00, i.e. the same as for a tape-based system, which means that most tape-based software can still be run from disc.

The Disc Filing System (DFS) ROM is ACP's own Advanced Electron DFS (AED), which is installed in one of two ROM sockets on the AP4. The other ROM socket is free to take a further Sideways ROM - it could be the Advanced DFS (ADFS), available from ACP soon. Removing the lid also reveals the 1770 disc controller chip, 8K of RAM for use by the AP4 and a well-designed and protected circuit board.

The AED provides all the standard DFS commands as well as a few extra ones including disc FORMAT and VERIFY. Also included are a few Master-type commands such as *DRIVE and *ROMS. The former allows you to read a 40-track disc on an 80-track drive, while the latter displays a list of ROMs installed in your Electron.

The great thing about a disc interface like this, used with a 5.25" disc drive, is its ability to run "standard" BBC Micro disc-based software. In fact, as long as software does not take account of BBC Micro hardware (such as Teletext and graphics chips), it should load and run with few problems.

The other point of note was its speed. While not comparable to a standard Beeb disc interface, it's certainly more than adequate and quiet in operation. Table 1 lists some timing results for a few programs I wrote to access the disc surface. Compared to its major rival, the Solidisk EFS, it comes out on top in four out of six tests. The timing, I should point out, were all taken with David Acton's stopwatch! Using the TIME function is not allowed, because to gain speed both systems seem to turn it off - or at least slow it down when performing any disc accesses. The AP4 works hard when in high resolution modes - to increase speed, the Solidisk EFS turns the screen off so it doesn't have to waste time refreshing the display. The AP4 tries hard to do both, but results in bad screen interference.

A useful 60-page manual is supplied which is both explicit and easy-to-read. If I was to find fault, it would only be because the manual does not go into disc theory or care, and for first time disc interfaces this could be a problem.

The AP4 is a very good product: Table 2 shows that it scores more points than the EFS. Remember that the EFS does some with 16K of Sideways RAM and includes a Winchester port which means that you can plug in a hard disc. However, for those of you looking for a disc upgrade for the Electron, the AP4 scores best - though at around £80 it is more expensive than I would have liked. In my opinion the AP4 should be considered as the standard interface for the Electron.