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On the topic of Linux and microkernels I highly recommend reading this old thread: Linus vs. Tanenbaum on the topic of microkernels vs monolithic ones.

I don't want to start the everlasting monolithic/microkernel flame war up again, but I think it's pretty clear that it's only the pace at which hardware has advanced in the last decade or so that has allowed Linux to continue monolithically.

There's a lot to be said for the microkernel architecture, and if Moore's Law ever does start to level off, then I think we're going to see a move away from monolithic designs for good. It's just not practical to keep stuffing more features into a monolithic kernel if you're not constantly getting more and more memory to run it on, and only a very small body of users can be expected to ever compile their own. (True, you can always recompile a specialized version of a monolithic kernel, ripping out all the stuff you don't need, but this is a PITA and it only becomes harder as the thing gets bigger.)

Along with probably most other Linux users, I've always wondered how things would be if Tanenbaum had released MINIX under a free license earlier in the game (Torvalds has said at several points that had MINIX been more free, he probably would have simply modified it, keeping its architecture, but since Tanenbaum had no interest in "turn[ing] MINIX in BSD UNIX" [1]...the rest, of course, is history.)

Or perhaps more interestingly, what would have happened if a free version of BSD had been produced for low-end hardware just a little earlier than it actually was. (In reality, 386BSD came out in a working form in July 1992 [so sayeth Wikipedia], nine months after the first Linux release, and 4.4BSDLite didn't come out until '94 [2].) It seems to me that had "real UNIX" been available for low-end systems in the early 90s, much of the impetus to create a from-scratch clone would have disappeared. (Although, maybe not; perhaps the philosophical differences that drive Linux and the BSDs in different directions would have eventually caused a from-scratch rewrite.)

Ultimately I don't think either alternative would really have brought us out at much of a different place than we are right now, at least from an end-user's perspective; the majority of users don't really care about kernels as such anyway. But it's always fun to play 'what-if,' as long as one keeps in mind that although it's easy to fixate on how things could be better, it could always be far, far worse.

[1] Great archive of Torvalds / Tanenbaum Usenet discussions here. There's so much ego going on there, from both sides, ASCII text can barely contain it...
[2] I'm partial to fellow Slashdotter connorbd's BSD History, which is a good primer.

I don't want to repost this old debate that I believe every geeks should have read it; but since nobody post it yet. I repost it for anybody who haven't read about this famous debate between Linus and Prof. Tanenbaum on microkernel.

Linus vs. Tanenbaum - "Linux is obsolete" Jan,1992

(Save your mod point for someone who really need them thanks!)

Not again:

http://people.fluidsignal.com/~luferbu/misc/Linus_ vs_Tanenbaum.html

We've got Andy Tanenbaum coming up with nothing practical in the fifteen or sixteen years he's been promoting microkernels, and then turning around and telling us he was right all along. Meanwhile, the performance of OS X sucks like a Hoover, as we all knew:

http://sekhon.berkeley.edu/macosx/intel.html

I'll just pretend I didn't see this article.

Actually he's been into boorish behavior from day 1 when it comes to microkernels. Namecalling between him and Tanenbaum (admittedly Tanenbaum is a bit haughty and provoking), and his slanderous accusations against microkernel researchers in general (a quote I can't find at the moment, but he basically accuses them all, as one big class, of academic fraud to procure grant money).

The only microkernel Linus knows jack about is Mach, an ancient piece of crap, which indeed is Linus indeed calls it. It's unfortunate real-world systems were saddled with it, and it's got real performance issues, but Linus carries on about it like Mach ran over his dog or something.

He conveniently ignores or chooses to remain ignorant of the fact that L4Linux is typically faster than Linux itself. To say nothing of the real-world success of QNX. And even L4Linux is pretty old by today's standards.

This is all pretty typical behavior of Linus: bluster now, bone up and learn, and implement it later. He did so with SMP (saying famously that the way to do it was one Big F**ing Lock, then learning that no this wasn't such a great idea after all). Then he went on a tirade about sun's /dev/poll before learning that yes they actually didn't cheat and they did it smarter, and Linux followed.

Ultimately, Linus and Linux come around. Sometimes he just has to vent.

  Linux is a kernel so shouldn't have any of those apps

Ah, no, Linus was definately not Tanenbaum's student. Quite aside from the fact that Tanenbaum taught in the Netherlands and Linus studied in Finland, we couldn't have this quote if he was:

I still maintain the point that designing a monolithic kernel in 1991 is a fundamental error. Be thankful you are not my student. You would not get a high grade for such a design :-)
--- Andy Tanenbaum

However, Linus did admit that at least one academic from his own university shared Tanenbaum's opinions, and thus he was unlikely to be getting high marks anyway. ;-)

As has been pointed to before, you can find an abstract of the famous "Linus vs Tanenbaum" posts to comp.os.minix here.

Linus is an engineer/tech. He dislikes theory work because it often gives nothing in practice.

Maybe that the time has come for Linus to take in some consideration the need for a change in the kernel code model. As of today it is released as a monolythic piece of software wheighing 27+ MB of compressed code (almost 240 MB when uncompressed).
If you add this to the complexity of an OS anyone can easily understand why a "partitioned" schema would greatly help the development.
Of course I'm also thinking about an oldish querelle between Linus and Andy Tanenbaum about monolythic kernel and microkernel approaches. I'm not talking just about this, but at least about partitioning of the code into (almost) independed units.
And maybe a microkernel approach could help to move in this direction: none can deny that both of them have a lot to teach about OSes.
Please, send flames to /dev/null.

Am I one of the few people who think that Tannenbaum won that debate?

That seems slightly more sensible than saying the Confederate States of America won the War of Northern Agression.

Tanenbaum opened the thread with a specific testable claim: that over the next 10 years, microkernel OSes would become dominant. He also said that writing Linux was "a truly poor idea".

Over the 13 years since the thread was posted, both of those predictions have been shown to be flat-out wrong. Maybe, at the time, Linus wasn't able to defend himself in English argument against a prestigious professional lecturer. But time has told who was really right.

Long ago, long before most folks were using Linux, Linus got into a fight with Andrew Tanenbaum about Linux and its design as a monolithic kernel. This is one of the more famous debates of linux lore, so it doesn't hurt read it and its annotations.

The quick summary is that Andy Tanenbaum proclaimed Linux dead way back in '92, saying, "While I could go into a long 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."

Linus on the other hand much preferred the monolithic design of linux, for a variety of reasons. Mr. Tanenbaum even went so far as to imply that Linux wouldn't be a passing project for his class. Ironic, no?

Even so, Tanenbaum did and still does have some good points about the Mach microkernel. I can't exactly imagine Torvalds is the most impartial judge of the mach microkernel.

Andrew Tanenbaum - Linus Torvalds TEACHER!

Not really. Andrew Tanenbaum was not Linus' teacher. Linus studied in Finland and Tanenbaum is teaching in The Netherlands.

...Andrew Tanenbaum, as seen on this page:

This IS possible. If a group of people wants to do this, that is fine. I think co-ordinating 1000 prima donnas living all over the world will be as easy as herding cats, but there is no legal problem. When a new release is ready, just make a diff listing against 1.5 and post it or make it FTPable. While this will require some work on the part of the users to install it, it isn't that much work. Besides, I have shell scripts to make the diffs and install them. This is what Fred van Kempen was doing. What he did wrong was insist on the right to publish the new version, rather than diffs against the PH baseline. That cuts PH out of the loop, which, not surprisingly, they weren't wild about. If people still want to do this, go ahead.

A bit of an inside joke from Linus, I guess... but now we can say he ripped off more than MINIX from Andy ;-)

First, I REALLY am not angry with Linus. HONEST. He's not angry with me either. I am not some kind of "sore loser" who feels he has been eclipsed by Linus. MINIX was only a kind of fun hobby for me.

For the rest of you who don't know 'the past' Prof. Tanenbaum with Linus, you may refer to the famous mailing list log "Linux is Obsolete".

Linus seems to be doing excellent work and I wish him much success in the future.

So I guess Prof. Tanenbaum can give higher grade than "F" to Linus now. :)

Both Prof. Tanenbaum and Linus are my favourite persons. I'm so happy to see this happy ending in real life. :~)

Tanenbaum took stabs at Linux. Torvalds took stabs at Minix. It turned into a famous flamefest.

Think someone is still sore about Minix's destiny compared to Linux's?

The reason for my frequent "no" was that everyone was trying to turn MINIX into a production-quality UNIX system and I didn't want it to get so complicated that it would become useless for my purpose, namely, teaching it to students. I also expected that the niche for a free production-quality UNIX system would be filled by either GNU or Berkeley UNIX shortly, so I wasn't really aiming at that.

Some of you may find it odd that I am defending Linus here. After all, he and I had a fairly public "debate" some years back. My primary concern here is getting trying to get the truth out and not blame everything on some teenage girl from the back hills of West Virginia. Also, Linus and I are not "enemies" or anything like that. I met him once and he seemed like a nice friendly, smart guy. My only regret is that he didn't develop Linux based on the microkernel technology of MINIX.

Torvalds Vs Tanenbaum. I've never used MINIX, but I believe the source code is out there somewhere, although AFAIK, it's not free software.

I've often wondered what things will be like when Hurd is ready, and we'll have GNU and GNU/Linux, and all those BSDs, and OS X all in usage.

And then we'll probably still have to worry about making stuff look right in IE 6, because Microsoft takes forever to update it.