From: bcr@cernapo.cern.ch (Bill Riemers)
Subject: OS vs SYSTEM TYPE (long) [OS]
Organization: CERN, European Research Center for High Energy Physics
Date: Sun, 13 Dec 1992 11:19:30 GMT


After reading through all those back articles in both comp.os.linux
and comp.os.bsd I've come to the conclusion the best thing for a
new user to do would be to install MSDOS, LINUX, and 386BSD on thier
computer.  However, it sounds like you have to reboot your computer
everytime you want to change your system type!  This might seem
reasonable until you stop and ask yourself what is the purpose of
an OS?  Mind you my understanding (mind you I am not a computer
scientist) is that an OS is what provides an interphase between
software and hardware for all programs.  That is why on an APOLLO
computer I can switch readily between the system types of 
BSD4.2, BSD4.3, SYS5.0, SYS5.3, and AEGIS without rebooting the
machine.  (Even without re-loging in.)  All of these system types
work through DOMAIN-OS.

So what is the problem?  It seems that both LINUX and 386BSD are
both OS's and system types.  Even worse, MSDOS just directly
interphases with the hardware without even using an OS!  So the
only system type supported under LINUX-OS is LINUX and the
only system type supported under 386BSD-OS is 386BSD.  Some 
people have already realized this and are working on a version
of MSDOS that use LINUX-OS.  Likewise, a simmular project is
being started for 386BSD. When they are done we will have:

  LINUX-OS supports LINUX, and MSDOS
  386BSD-OS supports 386BSD, and MSDOS


So the points I'm still confused about are:

 1. What in the world does OS2 support?

 2. Is there any work being done so that eventually we can
    have:

    *-OS supports 386BSD, LINUX, MSDOS  ?

   (I don't really care which type of OS * is as long its source
   code is publicly available and publicly distributable.)


The way this swapping of system type works on APOLLOs is:

   ver system-type command   ==> excutes one command in the
                                 selected system type

   ver system-type           ==> switches to the selected
                                 system type

The system SYSTYPE tells the OS what type of system you are
operating in.  So rather than having a root '/bin' directory, you have:

  '/sys5.3/bin'
  '/bsd4.3/bin'

then '/bin' is a symbolic link to '/$(SYSTYPE)/bin'.  The same thing
is done for all other system type specific directories.  So lets
say I want to write a script using sys5.3 commands.  Then I include
the following as the top two lines:

#! /bin/csh
ver sys5.3

What would be nice to be able to do the following on my PC:

#! /bin/tcsh
ver linux

-or-

#! /bin/sh
ver 386bsd

-or-

#! /bin/msdos
ver msdos6.0

                                     Bill


--
"Yeti!  Saw them in the London Underground twenty years ago.  Ghosts!
A headless woman used to walk through my bedroom at midnight.  Mermaids?
Grandpa was rescued from the Marie Celeste by one.  Vampires?  I always
wondered where my dad went to at night.  Telepathy?  Right now you're
thinking that I'm talking crap.  So what can you tell me that I won't
believe in?" - Andrew Hunt, "CAT'S CRADLE: WITCH MARK"
Newsgroups: comp.os.linux