dada wrote on 2022-01-18, 16:07:

Here's one of the few photos I have left of my monitor, albeit without a color test that shows any other shades unfortunately.

That photo clearly shows an MDA/Hercules text mode (9x14 font) so I'm guessing that you had a Hercules (or compatible) mono card and used a TSR such as SIMCGA. You get two "colours": normal and high intensity. Depending on how the monitor is adjusted, on a green phosphor CRT the high intensity can look somewhat white in colour.

Here's a bunch of photos showing what CGA games look like using various CGA simulators:
http://www.dosdays.co.uk/topics/cga_simulator … or_hercules.php

MDA monitors could also be driven with an EGA card. The result was a 640x350 pixel mode with three shades, including black.
It could also have been a dual-frequency screen, though. That would indeed support CGA graphics.

Oh wow, I'm actually really surprised by your answers. I always assumed that it was a CGA adapter, because that's what people always told me it was as a kid, and I had no reason to doubt them.

The thing is, though, we actually had a Hercules based computer as well, and that one was quite different from our "CGA". They both had the same games, but our "CGA" did not need to run HGCIBM.COM to play games whereas the Hercules one did. I also ran Leisure Suit Larry on both computers and the second one was clearly the Hercules version, and the first one was clearly not. That much I can remember clearly, and I also know they had different fonts. I can't deny that the font in my photo is wrong for CGA though, comparing it with the int10 fonts. Maybe Tulip, the manufacturers of the computer, installed a different font? At the very least, I know that our "CGA" worked out of the box with everything without the need for simulators.

Looking online, it seems Tulip used what's called a MAGDA (Monochrome and Graphics Display Adapter) card, and this online manual claims it has a "DGA" card that can matches both Hercules and CGA card features. I feel it has to be some variant of CGA in 4 color mode with the regular cyan/magenta merged into a single green color, at least on this monitor (a BM7502/00G).

Maybe this look is unique to these kinds of cards?

Does the system still exist, i.e. can you find out which type of video card is installed?
There were indeed a few any-standard-on-any-monitor cards that could display CGA graphics on an MDA monitor.
For instance, ATI had several in its "Wonder" series of cards.

Many of the turbo XT clones had graphics adapters that did both MDA and CGA modes, and were equipped with monochrome displays that could switch between the MDA and CGA frequencies, so you'd get a nice crisp MDA style text mode at the DOS prompt and normal CGA graphics (320x200 with 4 levels of mono intensity) when playing games. No need for CGA emulation TSR because the card's hardware supported CGA directly. The cards could autoswitch between MDA and CGA based on which BIOS video mode was requested. From a sampling of 5 mono CRTs that I've acquired, 2 of them are dual frequency MDA+CGA and 3 of them are MDA only, so it seems the multifreq mono displays were relatively common.

In CGA mode, the card is providing RGBI colours on the video connector, but the monochrome CRT is translating them into 16 shades of grey. So it's up to the display as to how it maps each CGA colour to a monochrome shade. (Also - to figure out if you have a dual freq mono display, check if the RGB pins connect to something inside the display...)

As a bonus - you get extremely crisp scanlines when displaying CGA's 200 lines on a mono display intended for MDA's 350 lines.