I had my doubts as to whether a "semi-industrial" even exists, but it's just what Singer called "industrial - for home use" or "light industrial". The first sign is the motor, which seems as fast as an industrial - quite remarkable for such a small motor. This actually makes it hard to do some things, like, well, sewing slowly, embroidery etc. Real industrial machines never have an attached motor.
Unlike the 630/730/830 it has a full rotary hook, and still a vertical bobbin so you can do embroidery (in theory at least).
Also it's a flat bed machine, and no cam stack. It says on needlebar that it can be converted into a full automatic machine. I just Googled for this and couldn't find what an automatic machine is. Singer use the same terminology: In the adjuster's manual for the 206/306/319 series, they only list the 319 as automatic. Now the biggest difference between the 306 and the 319 is that the latter has a cam stack, or built-in stitch patterns. My new Bernina doesn't have a cam stack so I'll assume this is what it means. To be honest cam stacks are nice but who really uses them? I don't use decorative stitches for anything but demonstrating them as a feature and never when constructing a garment, so they won't be missed. During garment construction I only ever use zig-zag and straight stitch, which brings me to another feature of this machine: The longest stitch is really very long! Haven't measured it but it's longer than any domestic I have.
OK, on to the machine's specifics.
Bernina 642-1. 1960, straight stitch and zig-zag, super fast, flat bed and Bernina green a-la 730. Here's a picture:
Didn't come with a manual but if the lady finds it she'll call me. They don't exist as free DLs anywhere on the Internet so if I get one, I'll scan it and make it available as a pdf, free of charge.
I'll update with cabinet pictures when dad has worked his magic.