into a new computing research department, while the operation of the internal computing resources, including the GE machines, moved to the computing services department. As a result, computing services tracked the computer usage internally with a cost system, meaning that each session of playing the game cost US$50 to US$75 on the internal balance sheet. Thompson learned that a neighboring department had an older, little-used PDP-7 minicomputer. This was equipped with a graphics terminal which gave it excellent graphics capabilities for the time. As this machine would solve the problems with playing the game, he ported Space Travel to this platform using a cross compiler on the GECOS system, writing the resulting machine code to punch tape and then loading it into the PDP-7. Thompson did not use any of the provided PDP-7 code, writing everything from scratch, including a floating point library and other low-level tools. The tedium of moving the code between the two machines prompted Thompson to design his own simple file system based on some chalkboard ideas by Dennis Ritchie and Rudd Canaday, rooted in their experience with the Multics file system. This, in turn, demanded some way to start the process running once loaded. More features were continually added to print, edit, delete and move files. Before long, it had become a simple operating system of its own. Thompson then wrote an assembler for the PDP-7 to avoid using the GECOS computer entirely. Legacy While Thompson continued working on the PDP-7, the original Multics team had concluded that as Bell had exited the Multics program, there was no reason for the company to continue operating the expensive GE 645, and they believed it would be removed within a few months. They repeatedly asked management for a new machine to continue their operating system work. This ultimately culminated in a lengthy proposal to buy some parts and rent others of DEC's new PDP-10 system, then US$120,000, but this too was rejected. Ritchie later surmised that the company had just exited one operating system project and was in no hurry to spend money to start another. In 1970, however, DEC introduced the PDP-11, which cost $65,000 and could be operated directly by the team without support from the computing services department. The team also changed their proposal; the machine was not being requested to develop an operating system, but a system for "editing and formatting text", essentially