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From: tsf@theory.cs.cmu.edu (Timothy Freeman)
Newsgroups: comp.os.minix
Subject: Re: MINIX VS XINU
Message-ID: <1010@theory.cs.cmu.edu>
Date: Thu, 22-Jan-87 12:12:39 EST
Article-I.D.: theory.1010
Posted: Thu Jan 22 12:12:39 1987
Date-Received: Fri, 23-Jan-87 07:22:05 EST
References: <3862@sdcrdcf.UUCP> <1053@ius2.cs.cmu.edu>
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Organization: Carnegie-Mellon University, CS/RI
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>In article <3862@sdcrdcf.UUCP> davem@sdcrdcf.UUCP (David Melman) writes:
>>I'm curious how the goals and purpose of Comer's Xinu operating system
>>(Operating System Design, the Xinu Approach) differ from Tanenbaum's Minix.
>>A few things they do have in common are:
>>	1) They both run on micros
>>	2) They both are a rewritten simplification of Unix
>>	3) They both are intended to be educational

I and several cohorts implemented a subset of Xinu for the IBM PC as a
project for an Operating Systems course back when I was at Rensselaer.  Here
are some differences between the two.  (I have no knowledge about
Minix except by reading this bboard, so my statements about Xinu are
going to be more accurate than my statements about Minix.)

    4) Minix is System V compatible; Xinu isn't meant to be a Unix, so
       it isn't compatible with anything.  (Xinu stands
       for Xinu Is Not Unix, and I can vouch for the correctness of
       its acronym.)
    5) Xinu only has lightweight processes (that is, they are all in
       the same address space and share a common pool of resources).
       Minix only has heavyweight processes (that is, each process has
       its own address space and can try to believe that it has its
       own pool of resources, to the extent to which this is true for
       Unices in general.)
    6) Xinu doesn't have an analogue to the exec system call, all code that
       you can ever execute must be in the initial core image.  Minix
       does have an exec call.
    7) Xinu specifies a new process to start by giving a subroutine to
       execute for the new process; it doesn't have a fork call.
       Minix does have fork.
    8) Xinu was not sufficient to use as a development system for
       itself.  Minix hopefully is.  (The original Xinu development
       environment ran under Unix and used cross-compilers.  The Xinu
       version I developed used MS-Dos as a development environment.)

In summary, Xinu is a great vehicle for an operating systems course
because it is possible for one person to implement enough of it to be
able to run things within a semester, but don't try to use it to get
any work done.
-- 
Tim Freeman

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