Tech Square was the nickname for the building at MIT which housed Project MAC, which later split into the AI Lab and the Laboratory for Computer Science (including the Dynamic Modeling, Mathlab, and Macsyma Consortium groups). The machine room was on the top (9th) floor.
The MIT-XX DECSYSTEM-20 TOPS-20 machine was installed where it says '1401'. The MIT-DM KA10 ITS machine was between the DM PDP-6 and the MIT-ML KA10 ITS machine, and also along the outer wall behind the PDP-6.
As the other end, the offices 919-922 were done away with, and that all became open raised floor, initally holding various robot arms, the Xerox Graphics Printer, etc, etc; later CADR Lisp Machines were there. The AI ITS KA10 was later replaced with the MIT-OZ TOPS-20 DECSYSTEM-20.