INMC 80 News

I have just finished a new version of SYS for the new double density disk card from Gemini, but this is not so important because the MOVCPM software provided with it is very good anyway. I have also created a special version for this disk card which has a “pseudo disk” which is really two 64K RAM cards on other pages, pretending to be a very high performance disk! I also look forward to seeing the new Nascom disk card, also double density, which is rumoured to be well under way.

Before criticising CP/M it is important to remember that much of its appearance to the user depends on how it has been implemented on a particular machine. I have seen several machines with errors or inadequacies in the CP/M implementation. Both users and suppliers then unfairly blame Digital Research for what is in fact a poorly written BIOS. To put both sides of the argument, CP/M is crude and unfriendly, but it is also a simple and effective means of providing a standardised software interface for a vast variety of good software, provided it is installed correctly.

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IMPORTANT NOTE for owners of Henelec/​Gemini G805 disk systems and Henelec FDC controller card kits using CP/M.

With the recent development of the Gemini G809 double density disk controller card, a defficiency in the original Henelec Format program has come to light. Two things about the Gemini G809 card have forced a change. Firstly, the G809 uses the more recent Western Digital WD1797 controller chip set, and secondly the G809 BIOS automatically selects between double/​single density on any drive other than drive A. The single density format is identical to the Henelec/​Gemini G805. This should mean that you can zap disks from the G805 into drive B of the G809 and PIP stuff in either direction with impunity. Unfortunately, the WD1797 senses which side of the disk is in use by picking up a ‘sides’ identifier byte slotted in the gap between the original track and sector identifiers of the G805 format. Now a disk formatted with the original Henelec software will not supply the ‘sides’ flag, so the G809 will think that the disk has only one side, with possibly disastrous results. To get round this problem a new format program has been written. This provides compatibilty with the G809, as well as providing a worthwhile 37 to 45% improvement in operating speed for G805 systems running at 4MHz without WAITs. This new format routine is available from Henry’s and Interface at a nominal handling charge of 50p to customers who wander in clutching a disk in their mits. Or 75p (plus the cost of a disk if you don’t send one) through the post.