Path: utzoo!mnetor!tmsoft!dptcdc!lethe!dave
From: dave@lethe.UUCP (Dave Collier-Brown)
Newsgroups: comp.unix.wizards
Subject: Re: Multics (was Re: getcwd() and friends.)
Summary: Ring crossings were/are fairly expensive
Message-ID: <2430@lethe.UUCP>
Date: 3 May 89 01:48:27 GMT
References: <4525@psuvax1.cs.psu.edu> <427@logicon.arpa> <1234@cs-spool.calgary.UUCP>
Reply-To: dave@lethe.UUCP (Dave Collier-Brown)
Organization: Systems Software, who runs MR12.3 on a z80...
Lines: 29


  Actually the cost of a system-call equivalent in Multics was/is
comparable to system calls in Unix, as one usually had a ring crossing
required to do anything major (ie, something other than returning one's
process id).  This meant calling a gate, having it double-check you, then
set up a new stack frame, then do the work.
  The old call sequence was...

	eaplp	-*,ic
	aos	2,ic
	tra	linq-*,ic*
	arg	0

  which means "do all sorts of stuff, then branch" (:-)).

  Seriously, though, there were lots of good, subtle ideas in Multics. Some
deserve to be reinvented.  Others deserve to be recorded as "classic, elegant
stupidity".


--dave

  

-- 
David Collier-Brown,  | {toronto area...}lethe!dave
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