Re: Microkernel architecture?

[David Leimbach <leimy2k@xxxxxxx>]

On Oct 8, 2003, at 12:22 AM, Gary Thorpe wrote:

> Yeah, an exokernel sounds cool...until you realize that every single  
> application needs to be linked into libraries that implement an OS  
> basically. What does that do for memory usage? How protected is the  
> machine from malicious/errant applications? Security? IPC?

Different strokes for different folks.  Some embedded systems only need  
to run 1 application ever.  So none of the above matters.

OS doesn't mean one thing to all people... nor should it.

> A microkernel makes it possible to modularize the OS, but an exokernel  
> sounds like it forces all the applications to be monolithic OS+app  
> hybrids. The speed comparisons on the ExOS web site don't even use a  
> particularly fast web server for BSD (or is NCSA now considered high  
> performance as well as obsolete?).

Yeah its like an embedded executive.  The whole focus is that you want  
the application to get all the resources it needs to do its job
as fast as possible.  At least that's always been my understanding.

Microkernels are a step in the opposite direction from that.

> Pedro Giffuni wrote:
>
> > This is off topic, (but just for reference and because there is not
> > technical-chat list ...)
> > when you mentioned you wanted a userland VFS API, I recalled someone  
> > already did
> > that: in fact, they turned everything into libraries and made the  
> > kernel very
> > small... they called it an Exokernel:
> > http://www.pdos.lcs.mit.edu/exo.html
> > They invented softupdates, BTW :).
>
>
> I believe Sun funding some research into improving FFS and the  
> resultant code first emerged on BSD:
> http://www.netbsd.org/Documentation/tune/5.html#a3
> http://www.netbsd.org/Documentation/misc/#softdeps
> http://www.mckusick.com/softdep/index.html
> http://www.usenix.org/publications/library/proceedings/usenix99/ 
> mckusick.html
>
> No mention of exokernels...was it used for the development?
>
> > cheers,
> >     Pedro.