I have a
feeling that some of the Sun3 line are like this too - and
then other Sun3's (like the 3/50, 3/60) weren't ever designed to
support a disk controller; they were simply diskless workstations.
I've never seen a -3/50 or -3/60 without a SCSI interface. Have you?
(It's the DD50F connector, and I think on that era of machine it's even
marked "SCSI".)
I'll second that. I borrowed a 3/60 from work for a while in the late
'80s, and it definitely has onboard SCSI. Same for the 3/50.