Microkernels (WAS RE: New to the list.)

[Sean Conner]

It was thus said that the Great Don Y once stated:
> Chuck Guzis wrote:
> >On 8/4/2006 at 9:56 PM Scott Quinn wrote:
> >
> >>Microkernels are neat in theory, but a well-trimmed monolithic kernel
> >seems to do pretty well with not too much space.
> >
> >Let me try that again.  NT 3.51 and earlier had the video drivers outside
> >of kernel mode.  When 4.0 brought them in as kernel mode, things got quite
> >a bit faster.  
> 
> Of course!  Each time you have to cross a protection domain
> you take a performance hit.  There's no free lunch.

  Ten years ago I remember one of the owners of Metrolink (who implemented
and sold commecial X servers) said that the *fastest* X server they sold ran
under QNX, a microkernel.  


> And it makes things so much easier to "load balance" in a
> multiprocessor design since you just move the thread to
> a different processor and let the magic do its thing
> (at a nontrivial cost, unfortunately).

  I also worked at a software company porting Unix utilities to QNX and I
really like QNX and what can be done with it.  I could use the modem on my
boss' computer to dial out without using *any* special software, just
specify the device on his computer (not only was the file system network
transparent, but you could use devices across the network).  You could even
run a program on one computer, pipe the output to another program on another
computer and send the output to a third computer, all from the command line,
and all possible because QNX was built on a microkernel and had all this
functionality built in.

  -spc (And the kernel on a Pentium based machine was only 8K
	in size ... yes, 8192 bytes in size ... )