Reply 1540 of 2128, by Scali
According to the PS/2 and VGA graphics book I have (the only one I have that even documents some of the MCGA registers!) the register set is more CGA-like than VGA. It has the VGA-like DAC registers (if fractint source code is correct), but also has CGA compatible CRTC registers with additional registers specific to the MCGA, and it has a "mode" register that is like CGA.
That is interesting. I wonder what it would make of 8088 MPH then, since it does a lot of CGA-specific CRTC/mode programming. It doesn't work on EGA/VGA at all of course.
The description implies that it only has 64KB of video RAM, and that video memory is mapped to B8000-BFFFF like CGA with B0000-B7FFF holding the character generator RAM in text modes (though in a very strange format).
I'm pretty sure it indeed has only 64k (enough for mode 13h), but also I'm pretty sure that it maps the video memory to A0000 in mode 13h, so that it is fully compatible there (as long as you stick to vanilla mode 13h of course, you can't do mode X hacks, scrolling etc).