The 3B1 AKA "UNIX PC" AKA "PC 7300" wasn't even Intel inside, it was Motorola 680x0. The true 3Bs (3B2/3B5/3B20) had WECO processors. (The first UNIX machine I used daily was a 3B20, in fact -- dog slow compared to the 680x0-based Sun 2s and 3s the cool kids got to use.)
The actual first UNIX PC (Intel processor) was the 6300 series, which were rebadged Olivettis. I ported a product line to the 6300 Plus, which at least had extended memory capability.
To the best of my knowledge, the 3B20D, a dual-processor fault-tolerant system running a UNIX variant called DMERT, was only used in the #5 ESS telephone switch - and was eventually replaced by an emulator running on a Sun system.
(I've seen a 3B21 living in a real running 5E within the last three years)
May the one that never had to deal with the A20 line or ask the keyboard controller for the favor of resetting the system throw the first stone.
When the mother board went bad AT&T sent a technician to my house to diagnose and replace it. For free.
Those were the old days of the lingering legacy of the way Bell did things.
Doing a demo where the phone rang and a notepad window popped up on its own was just short of voodoo. It didn't make any sense but I always privately fantasized Bell and Control Data would decide to get married and make a Plato terminal out of 7300s.
What amazes me more than anything else is the fact I'm still UNIXing for food nearly 40 years later.
It's both amazing and disappointing. It's amazing Unix is still used after almost 50 years. It's disappointing we never managed to come up with something better that was also viable.