Introduced in 1984. Successor of the PDP-11/23. At that time the components were VLSI, and these PDP-11's were marketed as MicroPDP's (this has in fact begun with the PDP-11/23). The PDP-11/73 had a 15MHz J-11 chip set-based CPU with 22-bit memory management for the 4MB RAM max. Just to make life more complicated, 18 MHz PDP-11/83 CPU boards can also be found in PDP-11/73 systems, as a PDP-11/83 CPU (M8190-A[DE]) with QBUS memory (instead of the PMI memory used in those systems) is called a PDP-/73...
There was no UNIBUS equivalent.
The J-11 was manufactured by Harris Semiconductors, and it hasn't been fully completed, it lacked the WCS and CIS options.
A very popular enclosure is displayed to the left: this was the BA23 standing tower configuration, that had place for a 8x4 backplane, an RX50 floppy or TK50 streaming tape drive and an RDxx harddisk. The BA23 could also be rack-mounted.