[HELP] How to write a simple Loader in ASM on MSDOS

[chants]

Just to clarify DOS was a 16 bit OS, based on 8 bit CPM. As for overlays there is a nice explanation of some of the details here: https://retrocomputing.stackexchange.com/a/25742 so you will need to know more than just the relevant MZ header fields as the interrupts and segmentation and all these things must be done correctly. In general overlays which are generally for limited memory systems are not needed in a modern context if you can recompile the original DOS program without them. It was designed in days RAM was scarce. That's why they don't exist in PE applications