some unfortunate PFY had to enter the code an opcode at a time by flipping switches on the front of the case
Don't know about BillG, but in high school in the late 1970s I was one of those PFYs. I worked summers for an academic research group that was doing bleeding-edge automated data capture and analysis from X-ray equipment and GC/mass spec machines using Altairs. (We also had some weird 12-bit computer from a company called Nuclear Data, IIRC.)
Program load was generally done from paper tape. If the machine got shut down or the power went off, though, none of that could happen until BASIC had been toggled in. I still have nightmares about trying to read crappy fifth-generation Xerox* copies of a mimeographed original of the switch positions. Is that an 8, a 5, or a 0? I dunno. If you're wrong, start over from the beginning...
The reward was an hour of wandering through "a twisty little maze of passages, all alike" in text-based D&D, on either a Teletype or (later) a glass terminal.**
* Yes, actual Xerox-brand photocopiers. Big as a house, and 2x as expensive.
** Get off my lawn, kids today have no idea, etc.