Microkernels (WAS RE: New to the list.)

Don Y dgy at DakotaCom.Net
Fri Aug 4 22:24:12 CDT 2006

Scott Quinn wrote:
>> But, one key difference between the QNX approach and that of
>> most other current OS's is the microkernel architecture.
>> Instead of a BIG monolithic kernel with ALL the drivers
>> installed (or, extra glue for LKM support, etc.), a microkernel
>> based design treats all of these as components which can be
>> plugged together.  And *talk* to each other (instead of being
>> invoked "from above").
> Yes, you just have the IPC overhead, though.
> Not sure if it's IPC or cheaper hardware, but large network operations on my Macintosh (System 10) bring the machine
> much closer to it's knees than any monolithic UNIX or even VMS on a VAX 4000/200. NB - I haven't used the microkernel
> based Tru64 yet.
> Microkernels are neat in theory, but a well-trimmed monolithic kernel seems to do pretty well with not too much space.

I think the "problem" with the microkernel approach is trying
to compare apples and oranges.  Getting a conventional UN*X
running on a microkernel architecture and trying to have that
compete *performance wise* with a monolithic kernel that
has been tweaked for MANY years is a no-win position.

The appeal of the microkernel approach is getting multiple
OS's to coexist on the same box (at the same time!) as well
as a cleaner conceptual design.

It also lends itself more cleanly to distributed systems
(which are difficult to implement using traditional
monolithic kernels which must make all the communications
very *visible* -- vs. their implicit roles in microkernel

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