As to your HIMEM issue when transmitting a bootstrap loader, I don't know the answer to your question, but seems like you could just POKE the HIMEM address directly instead of using CLEAR. It's at F5F4 on a model 100.
As an aside it's actually not completely correct to CLEAR whatever the header start address says. There could already be a programs in memory, i.e. the memory TS-DOS runs at may already be reserved. Or, the program that's already in RAM could be in conflict. Hence why things like TEENY.EXE can relocate TEENY to where it needs to be to stay out of the way of whatever else might be installed to RAM. Anyway, if you're assuming safety (no conflict) at the load address, you should probably still do a comparison, and if HIMEM is too high, then lower it. -- John.
