All sorts of tricks can be used. I remember using Monochrome RAM B000-BFFF in EMM386.EXE to save upper memory. Don't forget the ROM area that IBM PCJr carts use

All sorts of tricks can be used. I remember using Monochrome RAM B000-BFFF in EMM386.EXE to save upper memory. Don't forget the ROM area that IBM PCJr carts use. Commodore 64 had a lot of hacks, had a Mimic from Spartan that turned the Commodore 64 into an Apple II clone.