Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!udel!rochester!spot!bono!mikalsen
From: mikalsen@bono.uucp (Thomas Mikalsen)
Newsgroups: comp.sys.amiga.tech
Subject: Re: resource tracking
Keywords: What is a system call???
Message-ID: <315@spot.wbst128.xerox.com>
Date: 23 Feb 90 23:26:45 GMT
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Reply-To: mikalsen@bono.UUCP (Thomas Mikalsen)
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Last spring I took the Operating System Lab class here at RIT.  In the
class we broke up into groups of 3-5 and wrote a multi-tasking O.S.
on Sun-2s.  One of the big questions was: do we do it kernal based or
use message passing.  Well, being an Amiga owner, and knowing some of
the advantages to message passing, I liked the idea.  But, since
a kernal based os is easier to write (we had only 10 weeks) we
went with the KERNAL.

So what's my point??
Well, I wrote the windowing system for our OS.  It COULD NOT be done
in the kernal(loose to many interrupts).  So we added some simple IPC.  
The window system was just another task running (with certain privileges.)   
A call to the window-system invloved a stub (that ran in user context) that 
sent the message to the window system. 

A kernal-call, on the other hand,  involved a stub as well, 
but it trap-ed into supervisor mode and executed KERNAL code.

Both calls are "system-calls" if you consider the windowing part
of "The System."  Defining what your system is defines what a system
call is.  Maybe kernal-call is what some people mean by system call.
The term system-call describes the function of the call, NOT the
method of passing parameters.

This is just my opinion of course.

The big plus of message-passing and shared libraries is that parts of
the "system" can be added and modified with out having to re-make the
kernal (so long as there is a sufficent interface built into the
kernal already.)

Tom.
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Thomas  A.   Mikalsen		    "The gold is for us to capture all we want."
Rochester Institute of Technology 
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