Modularization and Hierarchy in a Family of Operating Systems
This paper describes the design philosophy
used in the construction of a family of operating 
systems. It is shown that the concepts of module and
level do not coincide in a hierarchy of functions. 
 Family members can share much software as a result
of the implementation of run-time modules at the 
lowest system level.
CACM May, 1976
Habermann,A. N.
Flon, L.
Cooprider, L.
