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From: guy@rlgvax.UUCP (Guy Harris)
Newsgroups: net.arch
Subject: Re: OS info request
Message-ID: <408@rlgvax.UUCP>
Date: Wed, 30-Jan-85 19:10:19 EST
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Posted: Wed Jan 30 19:10:19 1985
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> MPE on the HP3000 has no system calls.
> 
> System services are implemented in priveleged segments, and are
> called in the same way as any user subroutine. A segment is priveleged
> (can execute protected instructions) if it is compiled with 'option preveleged'
> and the owner of the file that it resides in has preveleged permission.
> 
> How would you rate this system?

By classifying all subroutines residing in privileged segments which are
intended to be called from non-privileged segments as system calls.
MULTICS worked the same way, although most "system calls" were NOT able
to execute privileged instructions; they merely ran in ring 0 (or 1) which
gave them access to more system data structures and access to the very
few routines which could actually execute privileged instructions.

Then again, somebody discussed RMS calls in VMS under the same heading.
In VMS, RMS happens to run in "executive" mode, but under RSX-11 it runs
in user mode as a regular library.  So are RMS calls system calls or not?

I think rating systems by the number of system calls is as useful as
rating processors by the size of their instruction set; i.e., not useful
at all.  Rate them by what you can do using that system, and how efficiently
and conveniently you can do it.

	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy