@blacklight As someone from that era, it was necessity. We had too little space to store code to run in too little RAM. So you rolled your own operating system. I did that to boot a supercomputer. I did that to cram more DAT code than would fit in CMOS to run in 16K with a paging operating system. I've calculated every tick of system clocks to ensure code finished in time for the next fetch. It's rocket science, sure. But really old rocket science on crappy hardware with cold solder joints.