Comment by af78

I had a similar experience of writing machine code for Z80-based computers (Amstrad CPC) in the 90's, as a teenager. I didn't have an assembler so I manually converted mnemonics to hex. I still remember a few opcodes: CD for CALL, C9 for RET, 01 for LD BC, 21 for LD HL... Needless to say, the process was tedious and error-prone. Calculating relative jumps was a pain. So was keeping track of offsets and addresses of variables and jump targets. I tended to insert nops to avoid having to recalculate everything in case I needed to modify some code... I can't say I miss these times.

I'm quite sure none of my friends knew any CPU opcode; however, people usually remembered a few phone numbers.