I still remember machine codes for PDP-11 instructions. I used clone of PDP-11 in my school: cheap school computer with two processors and 192KB of both main and video memory (UKNŠ”). Computer has built-in console debugger, so it was lot of fun to plug computer in and start typing programs in machine code, explore registers, co-processor memory, alter various tables, like font table to draw sprites instead of letters, etc. :-)
