Quoting Benjamin Walkenhorst (krylon@gmx.net):
...
> Now my problem is, I couldn't manage to open the case so far... ;-/ Until I 
> manage to, I hope you can help me a little in finding out, what kind of 
> machine this is and what Operating System I can run on it (NetBSD, I 
> hope...). But okay, what do I know besides its size? On the top-left corner, 
> there is a button saying "Siemens Nixdorf Quattro /40". On the top-right 
> corner there is another button saying "Nixdorf Computer AG Ident. Number 
> ...". I'm not gonna tell you that number, though... =)
> At www.computerarchiv.de I found something about Quattro/25, Quattro/30 and 
> Quattro/75 computers built by Nixdorf from about 1985 to 1995... But a 
> Quattro/40 is not mentioned. 

Nixdorf was a competitor to Pr1me through the 70's and 80s.  A
friend worked there as a "systems programmer" (I think it was system
admin stuff).

Deeply proprietary hardware.  Deeply proprietary software.  I might
liken it to getting a small IBM 360 or a 4 user AS/400.

At 75KG, with a little welding of some rebar, it should hold a boat
in a mooring quite nicely.