SITS

SITS means "Small ITS". Timesharing PDP-11 operating system created in the mid-1970s at MIT for running Logo.

Its design is vaguely reminiscent of ITS.

Like ITS, there is a SALV for managing disks, and DDT for debugging and running user programs.

SITS version 1146, and NSITS 111 and 112 have been preserved on a 1975 ITS backup tape from the AI Lab PDP-10.

AI memo 356 "Logo Progress Report 1973-1975" has this:

Originally Logo was implemented in assembly language on the PDP-10. In order to provide a computer system dedicated to educational use, it was adapted for the PDP-11. The first milestone in this direction was the completion in 1973-1974 of a dedicated timesharing system running 11LOGO.

The was not an entirely satisfactory solution because of the inability of the system to be self-maintaining or to run other languages or special purpose jobs (like a simulation environment or an educational real-time game). During 1974-1975, our programming staff, under the direction or R. Lebel, completed the design and implementation of a general purpose multi-language timesharing system for the PDP11/45. The SITS timesharing system was developed to provide an environment suitable for running Logo and other PDP11/45 programs. It incorporates a Multics-like tree structured file system including (potentially) full access control. It also provides unique capabilities for running programs as multiple process systems, rather than the more common single process approach, and the ability for each user to run many jobs simultaneously. The system include provisions for using both the older refreshed displays and our new raster displays.