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From: cur022@zodiac.ukc.ac.uk (Bob Eager)
Newsgroups: comp.os.misc
Subject: Re: Multics - Whats the current state
Message-ID: <20911.26eca5fd@zodiac.ukc.ac.uk>
Date: 11 Sep 90 08:53:17 GMT
References: <44101@<1990Aug30> <72900004@.Prime.COM> <20907.26e6edac@zodiac.ukc.ac.uk> <26665@bellcore.bellcore.com>
Organization: Computing Lab, University of Kent at Canterbury, UK.
Lines: 45

In article <26665@bellcore.bellcore.com>, martin@cellar.uucp (Martin Harriss (ACP)) writes:
>>segments, use page directories - you get 1MB 'segments' (in MULTICS terms)
> 
> Actually you only get *1024* segments (not 1Mb.)  I'm not sure that that would
> be enough for a 'real' system.

Sorry, what I intended here was that the 'segments' you get are 1MB in size;
I realise you only get 1024 of them. I believe that is enough in most cases,
since the limitation is per VM and not system wide.

> It also implies that you do relocation
> whenever you load an executable segment.  Not neccessarily a bad thing,
> but it does take time... Did Multics do this?  what about EMAS?
> 

Don't know about MULTICS, but EMAS did...that's the system I worked on. I'm
amazed to hear someone has heard of it! EMAS used a separate linkage area
which had to be relocated at load time; it wasn't very large, so the time
penalty wasn't too bad. It meant that shared code didn't have to appear in the
same place in every VM using it.

>>The use of the term 'segment' for the Intel 8088-style contruct (albeit bigger
>>on the 386) tends to push one's thinking in the wrong direction...
> 
> Actually, I think that the segmentation model, as implemented on the 386
> (as opposed to the 8086/66) is very powerful.

Agreed. I was only saying that the actual words used can be confusing.

> on a personal note:
> Hi, Bob. Still at UKC? I guess some things never change!
> 

Wait and see...

> Martin Harriss
> martin@cellar.bae.bellcore.com

Now I know why he's heard of EMAS!
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Bob Eager            | University of Kent at Canterbury
rde@ukc.ac.uk        | +44 227 764000 ext 7589
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