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> And I had an extra hercules graphics card that allowed me to debug on a separate monochrome monitor. For anyone wondering how that worked... Hercules graphic
by Jaruzel 7y ago
> And I had an extra hercules graphics card that allowed me to debug on a separate monochrome monitor.
For anyone wondering how that worked... Hercules graphics cards had their screen RAM in a different part of the memory map than CGA/EGA/VGA. So a bit of clever coding could get you 'dual screens' even at the DOS level.
There's a few YouTube videos showing ancient IBM XTs running with two simultaneous monitors - one CGA, and the other Monochrome.
- danparsonson 7y agoAs it happens it was also possible (although not really practical :-) to run two VGA cards in the same machine. The secondary card was left uninitialised by the boot process (since it would have conflicted with the primary), but it was possible to download the ROM, call into the initialisation routine (thus firing up the card and making it the primary), and thereafter switch which card was the one currently mapped into the PC address space to control which display you were writing to. Source: I managed to achieve it once, although only with a great deal of help from people on Usenet...
- lonelygirl15a 7y agoI had/have dual MDA and CGA compatible video cards in my 8088 PC, and used it extensively for debugging. There were debuggers that would run well on MDA, while the program displayed on the graphics adapter. Additionally, I soldered a pushbutton switch to the NMI and ground on the CPU, and hitting that would break out of whatever might be locking the system and give control back to the debugger. For the 80s, it was a delightful setup.