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The SITS Timesharing System

SITS means "Small Incompatible Timesharing System". It was a timesharing operating system for a PDP-11/45, created in the mid-1970s at MIT for running Logo.

AI memo 356 has this blurb: 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 PDP-11/45. The SITS timesharing system was developed to provide an environment suitable for running Logo and other PDP-11/45 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.

Installing SITS

Type ./build.sh to install SITS from binaries in the bin directory. The binaries were cross assembled from ITS. The automated scripts will format disks and install a basic system using paper tapes.

The SIMH emulator is compiled from source code; it may need some dependencies installed first.

Running SITS

Type ./run.sh to run SITS. Several windows will be opened which represent teletypes, vector displays, and raster displays.

Using SITS

Type ^Z to a teletype to log in, or Escape on a TV display. Log in as GUEST. Type : 0; . SLOGO to run Logo.

Useful commands in DDT are :HELP to see a list of commands, :SETD to set the current directory, :LISTF to list files, and :LOGOUT to log out. See the DDTORD file for more information.

Using Logo

Useful commands in Logo include CLEARSCREEN to start turtle graphics, and GOODBYE to log out. The 1974 AI memo 313 documents a slightly older version.

There are several different displays available:

  • To use a TV display, log in on a TV and type CS.
  • To use a vector display, log in on TTY 1 and type CS.
  • To use the 2500, log in on the 2500 TV display and type GTLDIS.