Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!aber-cs!athene!pcg From: pcg@cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.arch Subject: Re: Porting OSes (was DEC RISC Architecture) Message-ID: Date: 14 Oct 90 18:23:45 GMT References: <4462@trantor.harris-atd.com> <107038@convex.convex.com> <15007@hydra.gatech.EDU> <10734@pt.cs.cmu.edu> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 65 Nntp-Posting-Host: odin In-reply-to: lindsay@gandalf.cs.cmu.edu's message of 12 Oct 90 00:56:20 GMT On 12 Oct 90 00:56:20 GMT, lindsay@gandalf.cs.cmu.edu (Donald Lindsay) said: lindsay> The whole idea of porting an OS was new in the mid-70's: most of us lindsay> hadn't even considered it, until the first Unix port took place. Only because nbody knew about the MUSS thingie in the UK. OS-6 was also designed to be portable, but after Unix. MUSS antedates Unix by a lot, and was designed not just to be portable, but to support a heterogenous loosely coupled multiprocessor. References: Ibbett&Morris, "The MU5 computer System", MacMillan; Morris, Theaker, Capon, Frank, etc... "The MUSS operating system" etc..., SP&E, Aug. 1979. lindsay> Unix was suitable, not because its developers had allowed for lindsay> that - they hadn't - but because it was well done, and mostly lindsay> not in assembler. But Multics (written in PL/I) was well done, lindsay> and so was MCP (written in Burroughs Extended Algol). Why lindsay> Unix? 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 :-). lindsay> Perhaps the biggest (non-political) point was that Unix didn't lindsay> expect much from the underlying machine. The PDP-11 didn't lindsay> have much to give! And here we also have the biggest problem: current Unix implementations still mostly assume that common lowest denominator (vide Minix, Xinu). 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. It's difficult to be sure, but if we were to run Multics and SVR4/4.3BSD both on a GE 645 or both on a 486 or both on a MIPS, I think that Multics performance would be better. Not to speak of MUSS, that I saw running on a 68010 years ago, with performance well above that of 4.1BSD, of course. Incidentally, I think a lot of the sophistication in hw architectures is there only because of the pride and whim of the hw designer -- the 80286 has a very sophisticated architecture, where it must not be compatible with the 8086, but I cannot see it having it for anything resembling reasons of market demand. Ditto for many other similar cases, e.g. the MV/8000 rings, the Pr1me I32 mode, etc... "The soul of a new machine" I think is quite revealing on this (the 'no mode bit' struggle!). lindsay> I think there's a moral here somewhere. One of my morals is that hw designers have been *architecturally* far more advanced than OS designers, and this because of UNIX. I am sure that UNIX has evelevated the *median* level of OS use (by replacing loads of AOSes and RSXs out there), but certainly has set back the clock -- current generations of CS students assume that UNIX is all that there is to OS design, and this is a catastrophe, because it is about twenty years behind the state of the art. The beauty of UNIX lies in that its designers have made a particularly efficient compromise between what it should do and the limited resources offered by the hardware. In other words by a very good price/performance ratio at the low performance end of the spectrum. -- Piercarlo "Peter" Grandi | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcsun!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk