Back when I was a teenager, I would have absolutely gone down a rabbit hole like the author did. From "Upgrading and Repairing PCs" to reading all the technical manuals, usenet, etc. I definitely nerded out over this stuff! Glad to see folks still take an interest.
These days, I've an acquired brain injury. Between that an old age, it was a bit hard to read, but also, just a little bit familiar, so I enjoyed it.
Now I am expecting "256 color VGA programming in C" to resurface at some point! :D
320 x 200 CGA allows you to have only 4 colors at a time. Of course you can change the fixed palette on a certain scanline to have more colors. See for example California Games.
Yes, I did consider writing "4 colors", but thought someone would say "but you could have 16 colors on-screen" citing the early 80s titles which did scanline palette tricks. So, I went with "16 colors" as it was technically the upper-bound of 'official' documented colors (excluding composite artifact, dithering and other cool tricks). I didn't really want to get into explaining more since my goal was just linking the "8088 MPH" demo for the GP and anyone who hadn't seen it. Also, I have no idea if a technically correct, definitive and complete statement about CGA's maximum possible colors in a single English-language sentence is even possible.
But after wasting... oh, nearly ~800ms on this internal debate, I realized I'd already cleverly chosen to not link directly to the 8088 MPH video but instead a site containing both the video and links to explications revealing the myriad brilliant tricks and unnatural acts behind 8088 MPH. And from that rabbit hole, one may learn more than any mortal should know about CGA graphics. Especially apropos since the author of the OP was instrumental in creating 8088 MPH (although the OP's post is about BIOS things).
These days, I've an acquired brain injury. Between that an old age, it was a bit hard to read, but also, just a little bit familiar, so I enjoyed it.
Now I am expecting "256 color VGA programming in C" to resurface at some point! :D
Old hardware was always so much fun...