[kjs3]

I've hand assembled (small) bits of Z-80 code and toggled it via switches a byte at a time in to bootstrap old CP/M machines. Interesting, but not much fun.

Commercially, we commonly used cross assemblers or cross compilers and simulators that ran on minicomputers (like DEC VAXen). We could then burn the output to PROMs to put in the target machine for final debugging. Later we used a more specialized cross development environment (HP 64000 and Intel MDS) which had a big cable tied to a pod that plugged into the CPU socket on the target, allowing much more sophisticated debugging.