True, DOS and BIOS interrupt calls stopped your program until complete, this lag was however fairly consistent and in the order of a few milliseconds on newer m

True, DOS and BIOS interrupt calls stopped your program until complete, this lag was however fairly consistent and in the order of a few milliseconds on newer machines so could be used in higher latency real time control. "Proper" DOS real-time control generally used assisting hardware to buffer/offload processing or did not use the INT calls using interrupt driven system to make it real real-time, all DOS programs could be "Bare-Metal" if you did not use any DOS/BIOS INT calls which were generally written in assembly and not interrupt friendly. Also having no network stack or USB stack is pretty limiting these days. I'm sure FreeDOS can implement these, there are definitely DOS drivers out there for older network cards to get TCP/IP up and running and there was always serial modems which we used extensively in "the old days" (pause while audience cringes!) Being cut-off from the outside world is of course security bliss but the PC still needed to be physically secure as there were no passwords/encryption and remote maintenance is not an option.