Despite possible groans from aficionados or even cries of “shame!”, an improved version of the Z80-based PC-compatible could be prepared by those of a NAS­COM/​GEMINI background who are totally familiar with the excellent CP/M for the latter series of machines, on the assumption that their superior knowledge of DOS would enable them to optimise the application to a degree that is beyond my skills.

There remain vast quantities of CP/M machines among users; some exist in such numbers that they could support the developer’s expenditure of time and money on such an application, at end-user prices that are affordable to private owners, provided that the writer was prepared to sell directly, and not through a commercial company which adds large overhead charges to the cost.

A sizeable target for such an exercise would be the AMSTRAD PCW range on which a conversion would not be excessively expensive, even if the owner has to fit a 3.5″ drive, as well as buying the ZEDOS software. If anyone has the courage (or gall) to tackle the electronic and software problems, they could well become moderately affluent from servicing the needs of users who wish to acquire a home PC-compatible at half the price of even the poor AMSTRAD PC200; or even rich by extending the service to the rest of the world.

May I close by wishing ‘Good Luck!’ to my fellow travellers on MS-DOS’ ‘stony path’ the way things are going, you’ll need it! ●

A Warning

by Andrew Mead

The Hitachi 64180 is NOT fully compatible with the Z80. At least one pair of instructions set the flags differently. These are RRD and RLD, which rotate the lower 4 bits of the accumulator with (HL). In the Z80 the flags are set according to the result in the accumulator, whereas the 64180 sets them on the result of (HL). NAS-SYS ZNUM routine uses this instruction and if transferred to a 64180 system needs an ‘OR A’ instruction to set the flags correctly.

My present system alternates between a Nascom 2 and a GM880 CPU card, with the Nascom running both NAS-SYS/​POLYDOS and CP/M and the GM880 being CP/M only. A Winchester system always seemed too expensive, especially with a Xebec card, until I found one in the RS (Electromail) catalogue with SCSI interface built in. The GM829 floppy disk controller includes a SASI interface, but what is the difference. A read through the SCSI manual (from RS) suggested very little apart from an extended command set so I bought the Winchester. In the next issue