Was listening to the Dwarkesh Patel podcast recently and the guest (Agustin Lebron) [0] mentioned the book "A Deepness In The Sky" by Vernor Vinge [1]. I started reading it and a key plot point is that there is a computer system that is thousands of years old. One of the main characters has "cold sleeped" for so long that he's the only one who knows some of the hidden backdoors. That legacy knowledge is then used to…
His description of learning to be a programmer in that far future era was fun too, iirc there was just so much ‘legacy code’, like practically infinite libraries and packages to perform practically any function - that ‘coding’ was mostly a matter of finding the right pieces and wiring them together. Knowing the nuances of these existing pieces and the subtlety of their interpretation was the skill.
Another great example:
In Fire Upon the Deep, due to the delay in communications between star systems, everyone use a descendant of Usenet.