Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!aiai!tosh-km From: tosh-km@aiai.ed.ac.uk (ichi Maeda) Newsgroups: comp.arch Subject: Re: Porting OSes Message-ID: <3637@skye.ed.ac.uk> Date: 25 Oct 90 10:55:46 GMT References: <4462@trantor.harris-atd.com> <107038@convex.convex.com> <15007@hydra.gatech.EDU> <10734@pt.cs.cmu.edu> <10801@pt.cs.cmu.edu> Reply-To: tosh-km@aiai.UUCP (Ken-ichi Maeda) Organization: AIAI, University of Edinburgh, Scotland Lines: 47 In article <10801@pt.cs.cmu.edu> lindsay@gandalf.cs.cmu.edu (Donald Lindsay) writes: >In article pcg@cs.aber.ac.uk > (Piercarlo Grandi) writes: >>Somebody has said on these screens that a Multics port was considered or >>done, to some kind of 68K machine, and it would/did cost a few man >>years, that is peanuts :-). > >Since the somebody hasn't spoken up, I will point out that it was the >286/386, not the 68K. The difference is that the Intel hardware >supports call gates and hence is the only recent hardware that could >give Multics its protection rings. > >>We are still getting a PDP-11 related programming model on architectures >>designed to support Multicses. Recent Unixes are starting now to have >>some of what was introduced in Multics and MUSS *twenty* years ago. And >>I am quite sure that Multics twenty years ago was far more efficient >>that is SVR4/4.3BSD now. > >This claim of efficiency seems doubtful, since the two had different >missions and ambitions. There are things to regret (e.g. security): >but they are outside the purview of comp.arch. > >Multics needed hardware support for rings. The ring idea was long >ago replaced by capabilities - a concept that relates well to the >recent interest in objects. Some capability/object machines have >been built, and even sold. (Does anyone know how to characterize the >Biin machine?) HOWEVER, I have seen a number of success stories >where capabilities were supported entirely in software. It would be >interesting to discuss efficency, and portable OSes, in this more >modern context. >-- >Don D.C.Lindsay The essential hardware support for Multics is _segmentation_ rather than rings. Segmentation is important both for dynamic linking and resource sharing with the single level store. -- Ken-ichi -------------------------------------------------------------------- Ken-ichi Maeda, AI Applications Institute, University of Edinburgh, 80 South Bridge, Edinburgh EH1 1HN, United Kingdom. -------------------------------------------------------------------- JANET: Maeda@uk.ac.edinburgh ARPA: Maeda%uk.ac.ed@nsfnet-relay.ac.uk BITNET: Maeda%uk.ac.ed@ukacrl.bitnet UUCP: ...mcvax!ukc!ed.ac.uk!Maeda --------------------------------------------------------------------