Run CGA_COMP on any VGA, and see for yourself - http://www.oldskool.org/pc/cgacomp

Plain VGA only provides basic CGA compatibility - enough to run well-behaved CGA software, using BIOS calls.
Direct access to CGA registers doesn't work on a VGA, which means problems like bad palette, lack of certain effects, or even total garbage on screen.

So then most CGA games don't run? I would assume that a majority of them bypass dos/bios.

What about the PGC? How well did that emulate CGA? I assume the PGC didn't emulate MDA/Herc at all. Does the VGA run s/w intended for MDA/Herc?

kant explain wrote on 2023-11-15, 02:04:

So then most CGA games don't run? I would assume that a majority of them bypass dos/bios.

Majority of CGA games does run, but often looks different than intended.
This is a good list of titles likely to cause problems - https://www.mobygames.com/attributes/attribute/5/

Does the VGA run s/w intended for MDA/Herc?

MDA is text mode only, so no problems with VGA.
Hercules graphics, however, is impossible with plain VGA.

Of course, most VGA chips for ISA (and some for VLB and early PCI) supports special compatibility modes - both register-level CGA and Hercules.

+1

"Verde" (Spanish for "green") can re-program VGA cards to simulate the CGA experience.
Some sofware to do fake EGA scanlines?

Some utilities..
Re: Realtek realtalk, is it the best VGA for CGA? What is?

Edit:

So then most CGA games don't run? I would assume that a majority of them bypass dos/bios.

Grzyb already explained it, but I'd like to say that EGA/VGA have some dummy registers, essentially.

The basic things needed for handling CGA are all supported, but the special stuff might be just being ignored.

Things like Palettes, Composite Video (NTSC color burst), certain hacked text modes, attributes (blink/underline/bold) etc.

Then there are some other differences, like text-fonts used (CGA is using 8x8, which is evenly spaced), refresh rate etc.
https://int10h.org/oldschool-pc-fonts/fontlist/

Refresh rate on VGA is 70 Hz in 200/400 line modes, whereas CGA is using 60 Hz all the time (like EGA, derived from NTSC).
Or 50 Hz, sometimes, if the PC is a Soviet era clone with a synthetic CGA.

Hercules Monochrome uses 50 Hz, too (like PAL/CCIR).
Maybe relevant to know if using a CGA simulator on Hercules.

Last, but not least, some things are possible on VGA but not CGA.
On a VGA, it might be possible to do things in a CGA graphics mode that's not possible on a real CGA card.
Like freely changing background/foreground colours in certain CGA modes.

https://int10h.org/blog/2015/04/cga-in-1024-c … de-illustrated/

Edit: I hope that wasn't too much, I didn't mean to sound like a know it all.
There are people who know better than me, I'm just a user/tinkerer.