PDP-11 Booting
PDP 11/34 had a bootrom and an octal keyboard, which is kind of cheating.I grew up using the older PDP 11/45 where you had to key in (using binary toggles) a boot program.
Or, the way I did it, manually enter write address and byte count to the RK05 disk controller (memory mapped I/O) then writing a "01" Go command to RK05's command register and watch the RK05 disk activity light flicker briefly. Voila, RT11 was loaded. (This worked because on the PDP 11/45 DMA transfers from disk to memory worked also in CPU Halt mode.)