Re: [9fans] micro vs monolithic kernels

["John A. Murdie" <john@cs.york.ac.uk>]

Andrey A Mirtchovski <aam396@mail.usask.ca> wrote:
>i seem to remember reading somewhere a reasoning on why it was chosen to
>implement p9 with a monolithic kernel, instead of a micro one..

Charles Forsyth <forsyth@vitanuova.com> replied:
>the implied comparison is false.  to start with, the plan 9 kernel
>is not  `monolithic'.  it is highly modular.

I've heard people use the term `monolithic' to describe an operating
system that may or may not have been modular, but was a `monolithic
monitor'. Years ago, I was a junior on a project developing such a
operating system for business; it turned off device interrupts at the
start of execution of a system call and on again when the system call
was finished. Of course, this led to extremely large interrupt latency,
which was noticed when the time of day clock was observed to run slow!
The senior people on the project solved this by opening up ad hoc
interrupt windows in the code. This led to many disasters.

(No comparison with the Plan 9 kernel is intended, of course.)

John A. Murdie
Department of Computer Science
University of York
England