I'm reading the NE and PE file formats. they begin with a valid MS-DOS executable included entirely within the Win program. I know the DOS executables files format since a long time, but I have found nothing about the overlay files (.OVR/.OVL) used by some huge aplications in DOS. Their format is the same as the .EXE ones with some specific mistic differences that I couldn't find. I also do not know how does the operating system or the aplication use theese files, it is not a simple matter (like relocating). The funny part is that DOS compilers continue to support them, like the .EXE files.
Does anyone please remember anythig about those things forgotten a long time ago ? Anything would be usefull.