Only ACP has the cheek to call all its products 'advanced'. However, the label does usually fit. The A1770DFS is available for Master or B+ owners or Model B owers with 1770 upgrades, and provides all the functions of Acorn's 1770 DFS and lots more besides.

The A1770DFS is fully compatible with Acorn's 1770 DFS, and is as compatible with old DFS discs as that is. However, the A1770DFS can format and use double-density (MFM) discs, 'large format' discs (both sides of a disc treated as one), and 'large catalogue' (62 files) discs.

These extras are handled with extensions to the existing commands (such as *DRIVE 0 80 MFM), and clever automatic detection by the DFS.

An extension to the OPT command allows the formatting skew to be changed to suit your particular drives and to alter the disc options (Double/single density or automatic and read an 80 track drive as 80 track, 40 track, or automatically).

That alone is enough to warrant the 'advanced' title but the A1770DFS can also use Sideways RAM banks as a fast RAM disc, configured as drive number 8 (though this can be changed to any drive number). All the other commands can then be used as normal on this RAM disc.

As many sideways RAM slots as you want can be used as a RAM disc and they need not be in adjacent slots. The *SRRAMS command sets it all up. This system is much preferably to Watford's Silicon disc system that requires either the DFS or Silicon filing system to be in use at any time. Treating the RAM as just another disc makes it much more useful.

ACP have also implemented on this ROM a number of useful commands already available to 1770 Master users, and they have, quite sensibly, used the same command names as Acorn. Thus *APPEND will append entries to an EXEC file, and *SPOOLON will do the same with a spooled file. *CREATE can be used to generate an empty file of any specified length, while *MAP will tell you how the used sectors of a disc are distributed.

ACP's A1770DFS is obviously intended to replace Acorn's 1770 DFS, and for those model B and B+ users who are considering an upgrade but have not already purchased the standard 1770 DFS, it looks like a good buy since it appears to contain all of the commands that Acorn provide in their DFS, plus a few more. The RAMdisc must be seen as an extremely useful added bonus - all thrown in for free! - or almost.