PDPs are enormous computer units created by the Digital Corporation released in the 60s, that were s

PDPs are enormous computer units created by the Digital Corporation released in the 60s, that were sold mostly to scientists and engineers, with runs of under 800 units being popular. The PDP-1 was the center of the absolute prehistory of the hacker subculture as it emerged at MIT, and the first video game ever (Spacewar) ran on one. 

Fun fact: the man who managed the PDP has a weird comics connection, as he is the father of Astro City author, Kurt Busiek, who was a vice president at Digital in the 70s.