From mboxrd@z Thu Jan 1 00:00:00 1970 To: 9fans@cse.psu.edu, john@cs.york.ac.uk Subject: Re: [9fans] micro vs monolithic kernels From: "John A. Murdie" Message-Id: Date: Mon, 9 Apr 2001 15:33:15 +0100 Topicbox-Message-UUID: 7bf53122-eac9-11e9-9e20-41e7f4b1d025 Andrey A Mirtchovski 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 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