I feel like this is missing EMS and XMS memory. Both were well supported ways of getting more than 640k. EMS worked by page banking. 1 or 2 64k segments of memory would be changed to point to different 64k banks from an add on memory card. XMS just did a copy instead of a page bank IIRC. It's been a long time but I wrote DOS apps that used both to support more than 640k of memory using both standards.

https://en.wikipedia.org/wiki/Expanded_memory

https://en.wikipedia.org/wiki/Extended_memory

You should read the very first article I wrote in this “series” then, linked to from the opening paragraph: https://blogsystem5.substack.com/p/from-0-to-1-mb-in-dos (previously discussed in https://news.ycombinator.com/item?id=39031369 at the beginning of the year).

What "feeling" does it give you? ;) Borland Pascal and C++ support EMS overlays. Think of it like a shared library almost. Also, using DPMI is another way around it.