The Acorn Z80 second processor has jumped £100 in price to £399 - but what you lose on the swings you may gain on the roundabout, because the price of the BBC single disk has come down by £50 to £199 at the same time.

The Z80 board, launched in May (issue 61), comes with various items of bundled software besides CP/M 2.2 and GSX. It is the cost of supporting this software that has been the main cause of the price increase - for dealers to offer a reasonable service Acorn has had to give them larger margins.

The reduction in the 100K disk drive comes, Acorn says, from more efficient sources of supply and the need to remain competitive. It follows a bareful publicised reduction of £105 to the price of the 800K dual disk drive, which now costs £699.

Acorn's Z80 with two disk drives still struggles to be competitive with the Torch Z80 Disk Pack for price - Torch's ZDP240 gives 800K, a Z80, and bundled business software for £805. And for users assembling a business system around a BBC Micro there is the further alternative of the Rade R50 board (issue 76), which lets you pick the software you want. Acorn has no plans at the moment to offer a Z80 unit without the accompanying software.

The Acorn Z80 second processor has been selling 'by the thousand' every month, a company spokesman said. Where the BBC is being used as the hub of a business system Acorn aims to get as close as it can to the mainframe/minicomputer idea of a turnkey system, where you simply set it up, plug in and go.

But CP/M is popular enough to offer its own alternatives.