In preparation for a talk on Seventh Edition Unix this fall, I stumbled upon a service list from DEC for all known PDP-7 machines. From that list, and other sources, I believe that PDP-7 serial number 34 was the original Unix machine.

Today, Unix and its derivatives make up the majority of operating systems currently in use and its popularity continues to spread as the popularity of open-source software grows. All thanks to Kenneth Thompson, Dennis Ritchie, and their fellow rebellious Bell Labs colleagues, who—by refusing to watch their beloved Multics die—ensured that their Unix operating system would go on to run the world.