A friend worked in cpu engineering at IBM in the early 80's. He recalls that there was a very fast microcontroller known as "the 5 bit engine" that ran its instructions several times faster than the contemporary 3033 and 3081 370-range mainframes it was used with. It was used as the microprogram core of the desk-sized IBM 3060 operator and maintenance console of the 3033. Its speed apparently caused as much of a stir among IBM engineers as the 801 risc project. Google does not find much about this speed demon. On comp.arch in 1999, Julian Thomas responded to Del Cecchi's comment about IBM microcontrollers with
"Then there was the infamous 5 bit engine used in the 303x consoles!"

My friend recalls this engine as having a 7nsec instruction time. And that engineering teams resisted using its approach to build fast microcoded 370's instead of lots of hardware.

What was this amazing thing? How was it so fast? How was it used? Did it need water cooling, also? What were the reasons to not use similar techniques for the mainframes themselves? Could a similar design be used in our latest cmos chips, with similarly fast single-thread results?