Linus contra microkeernel

Linux is obsolete
Andy Tanenbaum
From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.minix
Subject: LINUX is obsolete
Date: 29 Jan 92 12:12:50 GMT
Organization: Fac. Wiskunde &h;Informatica, Vrije Universiteit, Amsterdam

I was in the U.S. for a couple of weeks, so I haven't commented much on LINUX (not that I would have said much had I been around), but for what it is worth, I havea couple of comments now.

As most of you know, for me MINIX is a hobby, something that I do in the evening when I get bored writing books and there are no major wars, revolutions, or senatehearings being televised live on CNN. My real job is a professor and researcher in the area of operating systems.

As a result of my occupation, I think I know a bit about where operating are going in thenext decade or so. Two aspects stand out:

Microkernel vs Monolithic System
Most older operating systems are monolithic, that is, the whole operating system is a single a.out file that runs in'kernel mode.' This binary contains the process management, memory management, file system and the rest. Examples of such systems are UNIX, MS-DOS, VMS, MVS, OS/360, MULTICS, and many more.
Thealternative is a microkernel-based system, in which most of the OS runs as separate processes, mostly outside the kernel. They communicate by message passing. The kernel's job is to handle the messagepassing, interrupt handling, low-level process management, and possibly the I/O. Examples of this design are the RC4000, Amoeba, Chorus, Mach, and the not-yet-released Windows/NT.

While I could go into along story here about the relative merits of the two designs, suffice it to say that among the people who actually design operating systems, the debate is essentially over. Microkernels have won. Theonly real argument for monolithic systems was performance, and there is now enough evidence showing that microkernel systems can be just as fast as monolithic systems (e.g., Rick Rashid has...