The thing was, that upper memory wasn't just for TSRs. Anything one can shove there, would happily stay there and run just fine.
My journey towards the most free, conventional memory ended at 637k on my 386 DX-33 with 8megs of RAM and a SoundBlaster card, with everything possible being shoved to high memory. Mouse driver, MSCDEX and even COMMAND.COM.
637k. So proud, much wow!
Good times!
I ended up making batch files that swapped around autoexec.bat and config.sys files so they could run.
If you remember seeing how, you'll get a free virtual cookie.
https://en.wikipedia.org/wiki/DOS_Protected_Mode_Interface https://en.wikipedia.org/wiki/Virtual_Control_Program_Interf...
I remember toying with DPMI in assembler.