Spacewar is one of the very first digital computer games, originally developed in 1962 at the Massachusetts Institute of Technology to run on a DEC PDP-1. For a sense for how significant this event was in the history and culture of computers, you need only read Steward Brand's excellent article Spacewar: Fanatic Life and Symbolic Death Among the Computer Bums written for Rolling Stone in 1972. Steward Brand's role in the history and culture of computers may be even more interesting than that of Spacewar itself.
MIT is returning to its historical roots in a fashion. The GAMBIT Game Lab has undertaken a project to re-implement the original game on an Arduino system. This effort involves investigating at a very low level the original Spacewar source code. The students involved have documented their experience. It's clear that the system constraints of the day motivated a far different style of development than is prevalent now.
Computer game development is now entering its sixth decade. Reaching back in time to unearth games is a peculiar form of archaeology. If source code for a given game is available, unlike most historical artifacts, it's in pristine condition giving a unique perspective on the technology and engineering of the time.