G809 FDC
This floppy disk controller card is capable of either single or double density operation. At the time it was produced the WD1797 control IC was a very new device. It will give about 160k of storage per drive in single density mode or 350k in double density mode (based on 35-track double-sided disk drives). Three software systems were available for this board:

D-DOS, a “floppy tape” OS treating the floppy as a tape.


g809 roms

CP/M 2.2 for modified NASCOM systems

CP/M 2.2 for Gemini “Multiboard” systems

The reason for having two different versions of CP/M is because the NASCOM and Gemini systems differ in video, keyboard and I/O support systems.

As far as I know at the moment, POLYDOS left the NASCOM memory map alone. Much existing software continued to run as before. CP/M required that the memory map be re-arranged. This prevented existing software from running, but allowed access to CP/M software.

As CP/M expected a screen size of 24 lines of 80 characters the user almost always had to use a separate video board as part of the system.