What is this unknown to me HDD (IDE?) controller in slot 7 of this //e?

Just another item you can´t google...
no problem for an expert like you.....
just a hint:
the manual issues the most important information:
The Mega Core system from Frank & Britting was
rather common system in 1985 to 1987.
It supported 5, 10 and 20 Megabyte harddisks
and up to 4 Head disksystems and it also supported
use with DOS 3.3, UCSD Pascal 1.1 and 1.2 as
well as ProDos up to 1.1.1 and CPM 2.20B 56 K.
It was possible to install all 4 OS-sytems beside each other
in own partitions.
If you view magazines from Germany of that time you
will recognize a lot of adds from that company.
speedyG

Frank & Britting was also selling in Great Britain, France, Italy and Spain....
and of course also placed ad´s in the english, french, italian and spanisch magazins....
i even remember about ad´s in the nibble magazin in USA...

Obviously their ads were ineffective or prices not very competitive since almost nobody has paid attention to this German company...

If so, it appears you are now able to do that.
A brief search also pulls up the ROM images from the MegaCore card from several different sites. While not necessarily helpful, perhaps that means some other information will be available (the German Wikipedia even mentions the company and their drives)
Zan

If you had read it, you'd know I was A) attempting to get back on topic, to let you know that ROM images for the card were available online so hopefully C) there might be more information about the card out there. Just like I said in my post.

Best of luck finding more information on the card.
Zan