Use some finer pitch graph paper and people could author "boot sector code" by literally coloring in the little squares with the necessary bits!
Would be sort of like paper tape.
Pepperidge Farm remembers when high-school computing classes used Scantron-style optical mark cards...
https://commons.wikimedia.org/wiki/File:HP_Educational_Basic...
Shame I used to have an SCSI scanner but I already disassembled it for parts.
One can write a simple bootloader, which reads bytes printed on a paper sheet to memory then boots it. Something like: black (0), white (1) or long rectangle (1), short rectangle (0). Wonder about the storage capacity of the A4 paper.