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From: darrell@sdcsvax.UUCP
Newsgroups: mod.os
Subject: Re: Why no "real" distributed systems?
Message-ID: <2733@sdcsvax.UCSD.EDU>
Date: Tue, 17-Feb-87 17:51:06 EST
Article-I.D.: sdcsvax.2733
Posted: Tue Feb 17 17:51:06 1987
Date-Received: Wed, 18-Feb-87 22:52:26 EST
Organization: Apollo Computer, Chelmsford, MA
Lines: 62
Approved: mod-os@sdcsvax.uucp

In article <2693@sdcsvax.UCSD.EDU> darrell@sdcsvax.uucp (Darrell Long) writes:

>What, exactly, IS a distributed system?  How does it differ  from
>a  system such as, say, 4.3BSD?  Will any of the current academic
>projects see wide acceptance, like MACH or the V-System?

A good description of distributed operating systems can be found in:
Tanenbaum, A. S. and van Renesse R. 1985.  Distributed Operating Systems.
ACM Computing Surveys 17, 4 (Dec.) 419-470.
    
Different people have different definitions for what defines a distributed 
system.  The primary criteria for establishing a distributed system are:
    1) transparency of file access / naming
    2) transparency of process execution
    3) transparency of protection / system accounting

The key concept is the transparency of operations across the machines that
consitute the distributed system.  

Bsd4.3 is not a distributed system.  It does not meet any of the criteria
we note above.  
    1) file access is not transparent.  In order to access a remote file a 
        special command must be executed in order to transfer the file to 
        the local host (e.g., rcp, ftp).

    2) Process execution is not transparent.  Special commands must be executed
        in order to get a process running on a remote host (e.g., rsh, rlogin).
        Execution of these commands further requires the use to be aware of
        which host they desire to access.

    3) System accounting is not transparent.  Each machine administers its own
        passwd file.

Apollo's Domain system is much closer to a commercial distributed system.
It supports transparent file naming and transparent system accounting.  
A Bsd4.2 and a System 5 UNIX port is co-resident with Apollo's Aegis kernel.
This allows any unix program to take advantage of the distributed resources
naturally.

At this time Apollo's system does not yet support transparent process 
execution, but its implementation of the Network Computing System provides
considerable leverage for the development of fully distributed applications.
The Network Computing System (NCS) is a portable system composed of an 
RPC mechanism (complete with an interface description language and compiler 
for the automatic generation of client and server side stubs); and a 
location broker which allows applications to dynamically determine the 
location of transient objects.


- Joe Pato
  Apollo Computer Inc.
  apollo!pato@mit-eddie.arpa

* Network Computing System and NCS are trademarks of Apollo Computer Inc.
-------


-- 
Darrell Long
Department of Computer Science & Engineering, UC San Diego, La Jolla CA 92093
ARPA: Darrell@Beowulf.UCSD.EDU  UUCP: darrell@sdcsvax.uucp
Operating Systems submissions to: mod-os@sdcsvax.uucp