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SubjectRe: Some very thought-provoking ideas about OS architecture.
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In article <Pine.LNX.4.03.9906201138390.534-100000@mirkwood.nl.linux.org>,
Rik van Riel <riel@nl.linux.org> wrote:
>Unfortunately, EROS is still based on the PC hardware as
>we've got it today and not modeled after a JINI-like
>appliances model (the network is the computer).
>
>With the death of the monolithic computer (if it happens)
>will come the death of Unix, Windows _and_ EROS.

That's a classic thing said by "OS Research People".

And it's complete crap and idiocy, and I'm finally going to stand up and
ask people to THINK instead of repeating the old and stinking dogma.

It's _much_ better to have stand-alone appliances that can work well in
a networked environment than to have a networked appliance.

I don't understand people who think that "distribution" implies
"collective". A distributed system should _not_ be composed of mindless
worker ants that only work together with other mindless worker ants.

A distributed system should be composed of individual stand-alone
systems that can work together. They should be real systems in their
own right, and have the power to make their own decisions. Too many
distributed OS projects are thinking "bees in a hive" - while what you
should aim for is "humans in society".

I'll take humans over bees any day. Real OS's, with real operating
systems. Monolithic, because they CAN stand alone, and in fact do most
of their stuff without needing hand-holding every single minute.
General-purpose instead of being able to do just one thing.

>At the moment I can see only one Open Source system that
>could become ready for a world like that. Alliance OS
>(http://www.allos.org/).

I will tell you anything based on message passing is stupid. It's very
simple:

- if you end up doing remote communication, the largest overhead is in
the communication, not in how you initiate it. This is only going to
be more true with mobile computing, not less.

Ergo: optimizing for message passing is stupid. You should _always_
optimize for the local case, because it's the only case where the
calling protocol really matters - once you go remote you have time to
massage the arguments any which way you like.

- Most operations are going to be local. Any operating system that
starts out from the notion that most operations are going to be
remote is going to die off as computers get more and more powerful.

Things may start off distributed, but in the end network bandwidth is
always going to be more expensive than CPU power.

- Truly mobile computing implies that a noticeable portion of the time
you do _not_ want to be in contact with any other computers. Your
computer had better be a very capable one even on its own. Anybody
who thinks anything else is just unbelievably misguided.

This implies that your computer had better have a local filesystem,
and had better be designed to work as well without any connectivity
as it does _with_ connectivity. It can't communicate, but that
shouldn't mean that it can't work.

So right now people are pointing at PDA's, and saying that they should
be running a "light" OS, all based on message passing, because obviously
all the real work would be done on a server. It makes sense, no?

NO. It does NOT make sense. People used to say the same thing about
workstations: workstations used to be expensive and not quite powerful
enough, and people wanted to have more than one. Where are those people
today? Face it, the hardware just got so much better that suddenly REAL
operating systems didn't have any of the alledged downsides, and while
you obviously want the ability to communicate, you should not think that
that is what you optimize for.

The same is going to happen in the PDA space. Right now we have PalmOS.
It's already doing internet connectivity, how much do you want to bet
that in the not too distant future they'll want to offer more and more?
There is no technical reason why a Palm in a few years won't have a few
hundred megs of RAM and a CPU that is quite equipped to handle a real
OS. (If they had selected the strongarm instead of a cut-down 68k it
would already).

In short: message passing as the fundamental operation of the OS is just
an excercise in computer science masturbation. It may feel good, but
you don't actually get anything DONE. Nobody has ever shown that it
made sense in the real world. It's basically just much simpler and
saner to have a function call interface, and for operations that are
non-local it gets transparently _promoted_ to a message. There's no
reason why it should be considered to be a message when it starts out.

Linus

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