|1988. Based on the J-11
chip, DEC originally wanted the clock speed to be 20MHz, but it couldn't
be done on time, so the actual speed was 18MHz. It was the fastest CPU
of the -11's anyhow. The high-end configuration had 4MB RAM on PMI (Private
Memory Interconnect) and a floating-point accelerator.
The UNIBUS-based /84 was for those customers, who wanted to use legacy equipment: it was the same (qbus) CPU board with a KTJ-11B UNIBUS adapter. Despite this, the 11/83 had significantly higher I/O bandwidth than the 11/84, because the qbus had been revised by then with block mode, the ability to send a burst of data with a single address phase. This burst rate exceeded any UNIBUS implimentation.
The box on the picture to the left is a BA123 which was a popular enclosure for qbus machines. Apart from the 12x4-slot qbus backplane, it had five slots for storage units, e.g. room for two or three harddisks, a tape drive (TK50 here) and floppy.