alt Hacker NewsI started out writing machine code without an assembler and so had to hand assemble a lot of stuff. After a while you end up just knowing the common codes and can write your program directly. This was also useful because it was possible to write or modify programs directly through an interface sometimes called a "front panel" where you could change individual bytes in memory.
Back in 1985 I did some hand-coding like this because I didn't have access to an assembler: https://blog.jgc.org/2013/04/how-i-coded-in-1985.html and I typed the whole program in through the keypad.
Same here. On/For the ZX Spectrum, looking up the hex-codes in the back of the orange book. At least it was spiral-bound to make it easier.
Later still I'd be patching binaries to ensure their serial-checks passed, on Intel.