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. (See Henelec/G805 system for more information).

 

POLYDOS 2

g809 roms

POLYDOS left the NASCOM memory map alone. The screen memory and monitor workspace didn’t change and much existing software continued to run as before.

 

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.

CP/M required that the memory map be re-arranged as it requires free memory from 0000H – where the monitor is normally situated. This prevented existing software from running, but allowed access to CP/M software. A new PROM was used to remap the system on a Nascom 2.

As CP/M expected a screen size of 24 lines of 80 characters the user had to install an IVC (or similar) video board as part of the system.

GM809_Manual_SecondIssue

GM809_Manual_Software

GM809_Circuit


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