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SubjectRe: Some very thought-provoking ideas about OS architecture.
On 20 Jun 1999, Linus Torvalds 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).
>
> That's a classic thing said by "OS Research People".

Which I'm not :)

> I don't understand people who think that "distribution" implies
> "collective".
>
> A distributed system should be composed of individual stand-alone
> systems that can work together.

OK. I can agree with this. Still, Bill Joy can't be alltogether
wrong, can he? This is somewhat of a dillemma -- having to choose
between the paradigms of Bill Joy and Linus Torvalds... :)

> >(http://www.allos.org/).
>
> I will tell you anything based on message passing is stupid. It's
> very simple:
[communications overhead is either in the actual communication
channel or unneeded]

The Alliance OS uses something like a shared library so that
what looks like message passing from higher levels only is
message passing when it needs to be -- otherwise the higher
overhead is avoided.

> - Most operations are going to be local.

Optimizing for the local case doesn't mean that remote operations
can't be made transparent. Because of latency problems, you are
probably right though...

> - 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.

It depends. If a computer is used as a way of getting at information,
then you will want it to be connected. Mobile phones simply aren't
very useful on the north pole, however well they might function on
their own. Computing is more and more about communication and not
about number-crunching or playing games -- which, I agree, can be done
very well without network access.

Even for things like a calendar you will want access to outside
information. If you plan an appointment with someone else, you
need to be able to communicate with eachother to agree on a date/time
both of you are able to meet...

> 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.

It can help achieve things we can't do with Linux:

Upgrade (parts of) the OS while running.
Since message passing objects are self-contained, you can
replace them more easily than possible with 'classic' OSes.
User process migration and other nice scalability and/or
reliability tricks are also more easily done.

Transparent networking.
While userland can do this in a library, this feature can be
very useful to achieve high availability because it makes
clustering at the filesystem level extremely easy (to name a
thing).

Sandboxing parts of the OS.
Finally it's possible to test new kernel parts without risking
the rest of your system. Debugging a new networking library
(kernel-level, that is) without endangering the rest of the
system to stray pointers. The sandboxing protection can always
be removed later when the new kernel addition has been found
to work properly.


While I agree with your point that computers will be both powerful
enough to do anything and never powerful enough not to need the
maximum level of optimization (this seemed to be what you were
saying and, however paradoxical it may seem, will probably be true
forever), I think you should take a more positive attitude towards
new system concepts.

Even if you don't like them, some very nice and useful spinoffs
could come from the research in those areas. We need diversity
in order to select the best alternative for the job at hand.

I won't try to convince anyone to turn Linux into such a system.
Not only doesn't it make sense, I wouldn't even want Linux if it
became like that -- other systems can take on other roles that
are to be played in the huge playing field that's out there...

Rik -- Open Source: you deserve to be in control of your data.
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