It is an ST-506 MFM hard disk controller. Recognizable because of the 34 pin and quad 20 pin connectors, a 20mhz crystal
and a phase-locked loop for...
I've been going through a few hundred tapes, the only ones that I don't have to do much to are 3M 6150s and 600s that were written
in the early 90s....
System 3x hasn't been of interest to hobbyists until pretty recently. Much has already been thrown out.
Programming documentation and languages like...