I strongly suspect that the big boxy terminal is hardware-specific and geared toward running maintenance tasks. We had such beasts on the STAR also--the Maintenance Control Unit (MCU) which was a dedicated 16 bit mini, complete with drum, with tentacles reaching deep into the CPU. It initiated system startup, among other things--you could modify any register or memory location, trigger various events, etc. One of my projects at CDC was development of an RS232 interface so that the system could be tinkered with remotely.
Don't want to go off-thread, but any quick pointers to STAR info?