In Falcon 3 if you didn’t have enough “low” RAM (the under 640k part), B-52s had no windows on the front, among other lost details.
So many of us made custom autoexec.bat and config.sys for playing F3 that would bypass loading drivers for CDROMs and such. We even found a super-slim mouse driver (it was like 8k resident) so we could use a mouse in the menus still without violating that limit.
I believe you needed to have 610k free (so mouse, system, and other drivers had to total less than 30k) or it was insufficient.
Many switched from MS DOS to DR DOS, or used QEMM386 instead of MS’ own EMM386 because they used less low RAM.