Ken Thompson, a programmer in the Labs' computing research department, had worked on Multics. He decided to write his own operating system. While he still had access to the Multics environment, he wrote simulations for the new file and paging system on it. He also programmed a game called "Space Travel", but it needed a more efficient and less expensive machine to run on, and eventually he found a little-used Digital Equipment Corporation PDP-7 at Bell Labs. On the PDP-7, in 1969, a team of Bell Labs researchers led by Thompson and Ritchie, including Rudd Canaday, implemented a hierarchical file system, the concepts of computer processes and device files, a command-line interpreter, and some small utility programs, modeled on the corresponding features in Multics, but simplified. The resulting system, much smaller and simpler than Multics, was to become Unix. In about a month's time, in August 1969, Thompson had implemented a self-hosting operating system with an assembler, editor and shell, using a GECOS machine for bootstrapping.