I recall reading _somewhere_ about some early PDP-11
memory management
 thing used on early PDP-11 Unix that supported the KE11 ... by having a
 small window that allowed user code access to the KE11. ...
 Does this ring any bells for anyone? 
Never mind - found it, it was in "Odd Comments and Strange Doings in Unix":
  
https://www.bell-labs.com/usr/dmr/www/odd.html
The memory management thing in question was the KS11; I looked, but could not
find anything about it. Does anyone know of anything?
        Noel