Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Personal OS
Message-ID: <1990May28.155933.20953@utzoo.uucp>
Organization: U of Toronto Zoology
References: <402@newave.UUCP> <3300131@m.cs.uiuc.edu> <9437@pt.cs.cmu.edu> <36849@think.Think.COM>
Date: Mon, 28 May 90 15:59:33 GMT

In article <36849@think.Think.COM> barmar@nugodot.think.com (Barry Margolin) writes:
>>In summary: if my workstation had a single address space, I'd sell it
>>and buy something adequate.  (Sorry, Ed.)
>
>Actually, one of the best reasons for a single address space is to simplify
>sharing of data between applications, which promotes integrated software...
>... It's true that integrated software can be written
>when the applications have walls between them, but it's harder and rarely
>very extensible...

There is no problem in writing integrated software on a multi-space machine,
you just do it all in one space and pretend that the walls don't exist.  On
the other hand, a one-space machine with flimsy protection makes it very
difficult to write multiple programs that are guaranteed *not* to interfere
with each other.

If you look at the software on the Alto, the system from which much of the
one-space mythology is descended, you find that there is no notion of
non-interfering parallel processes at all -- all parallelism has to be
preplanned -- and the only interprocess-communication method that works
between independently-written programs is the file system.

The very "wide" interface made possible by sharing all memory is a
two-edged sword.  It is very powerful for programs that want to cooperate
and are willing to work at it.  But it makes it very difficult for programs
to work together without such advance planning, precisely *because* the
inter-program interface is so versatile and powerful and demands that so
many choices be made.  The Unix approach, with independent programs plugged
together by a simple command interpreter, simply does not exist on many 
such systems.  The interfaces are too rich and too powerful for random
programs to talk to each other easily.
-- 
As a user I'll take speed over|     Henry Spencer at U of Toronto Zoology
features any day. -A.Tanenbaum| uunet!attcan!utzoo!henry henry@zoo.toronto.edu