
                 Mach-US: UNIX On Generic OS Object Servers


              J. Mark Stevenson                Daniel P. Julin
          School of Computer Science      ISIS Distributed Systems
          Carnegie Mellon University





                                  Abstract


This paper examines the Mach-US  operating system, its unique  architecture,
and the lessons demonstrated through its implementation.

  Mach-US is an  object-oriented multi-server OS  which runs on the  Mach3.0
kernel.   Mach-US  has a  set of  separate servers  supplying orthogonal  OS
services and  a library  which  is loaded  into each  user  process.    This
library uses the services  to generate the  semantics of the  Mach2.5/4.3BSD
application programmers interface (API).  This architecture makes Mach-US  a
flexible research platform and a powerful tool for developing and  examining
various OS service options.

  We  will  briefly  describe  Mach-US,  the  motivations  for   its  design
choices, and  its  demonstrated strengths  and weaknesses.    We  will  then
discuss the  insights  that we've  acquired  in the  areas  of  multi-server
architecture, OS remote method invocation, Object Oriented technology for OS
implementation, API independent OS services, UNIX API re-implementation, and
smart user-space API emulation libraries.

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