g809 roms

From a company called PolyData, this was an excellent alternative to CP/M for the Nascom computers. It had several advantages for those machines. Firstly, Nas Sys was retained. Secondly, the existing video system could be retained. There was no need to relocate either of these in memory so existing software could, in most cases run normally. Converting a system for CP/M, on the other hand, made it incompatible with all Nascom software.

The system memory map under PolyDos was:

0000 – 07FF    Nas-Sys monitor program

0800 – 0BFF   Video display memory

0C00 – 0FFF   Workspace, used by various programs

1000 – BFFF  Program area

C000 – CFFF   PolyDos workspace & overlays

D000 – DFFF   PolyDos EPROMs

E000 – FFFF   Nascom BASIC ROM

PolyDos was normally supplied on two 2708 EPROMs. You also got a big manual!

GM515  PolyDos 1 could be used with the G805 drive system

  • single or double sided, 35 tracks per side, single density only.

GM516  PolyDos 2 could be used with the G809 or G815 systems

  • single or double sided, 35 racks per side, single or double density. 350k per drive max.

GM533  PolyDos 3 could be used with the Lucas drive system

  • single sided, 80 track, quad density. Approx. 720k per drive

GM534  PolyDos 4 could be used with the GM825 disk system

  • double sided quad density drives, 400k per side / 800k per drive

You had to specify your disk system on ordering and the EPROMs would be set up appropriately.

The EPROMs clashed with the normal memory spaces used for ZEAP, the editor assembler, NASPEN editor and NAS-DIS disassembler. However, PolyDos was supplied with its own replacements, PolyZap, and a disk-based editor, PolyEdit, so this wasn’t too serious a problem. A disk BASIC was also included, which was an enhanced version of the standard Nascom BASIC. It was upwardly compatible and no changes were needed to programs written for Nascom BASIC.

PolyDos was written by Anders Hejlsberg (PolyData was his company in Denmark), who also wrote Blue Label Software Pascal for the Nascom-2. He rewrote this for CP/M and DOS as Compass Pascal and PolyPascal. Later it was licensed to Borland and integrated into an IDE to become the Turbo Pascal system.