Linus Torvalds in 2003

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Subject: LINUX is obsolete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 & 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 have a 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 senate hearings 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 the next decade or so. Two aspects stand out:

1. 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.

The alternative 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 message passing,

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 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.

The only 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 published papers

comparing Mach 3.0 to monolithic systems) that it is now all over but

the shoutin`.

MINIX is a microkernel-based system. The file system and memory

management are separate processes, running outside the kernel. The I/O

drivers are also separate processes (in the kernel, but only because the

brain-dead nature of the Intel CPUs makes that difficult to do otherwise).

LINUX is a monolithic style system. This is a giant step back into the

1970s. That is like taking an existing, working C program and rewriting

it in BASIC. To me, writing a monolithic system in 1991 is a truly poor

idea.

2. PORTABILITY

Once upon a time there was the 4004 CPU. When it grew up it became an

8008. Then it underwent plastic surgery and became the 8080. It begat

the 8086, which begat the 8088, which begat the 80286, which begat the

80386, which begat the 80486, and so on unto the N-th generation. In

the meantime, RISC chips happened, and some of them are running at over

100 MIPS. Speeds of 200 MIPS and more are likely in the coming years.

These things are not going to suddenly vanish. What is going to happen

is that they will gradually take over from the 80×86 line. They will

run old MS-DOS programs by interpreting the 80386 in software. (I even

wrote my own IBM PC simulator in C, which you can get by FTP from

ftp.cs.vu.nl = 192.31.231.42 in dir minix/simulator.) I think it is a

gross error to design an OS for any specific architecture, since that is

not going to be around all that long.

MINIX was designed to be reasonably portable, and has been ported from

the Intel line to the 680×0 (Atari, Amiga, Macintosh), SPARC, and NS32016.

LINUX is tied fairly closely to the 80×86. Not the way to go.

Don’t get me wrong, I am not unhappy with LINUX. It will get all the people

who want to turn MINIX in BSD UNIX off my back. But in all honesty, I would

suggest that people who want a **MODERN** “free” OS look around for a

microkernel-based, portable OS, like maybe GNU or something like that.

Andy Tanenbaum (ast@cs.vu.nl)

P.S. Just as a random aside, Amoeba has a UNIX emulator (running in user

space), but it is far from complete. If there are any people who would

like to work on that, please let me know. To run Amoeba you need a few

386s, one of which needs 16M, and all of which need the WD Ethernet card.

From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)

Newsgroups: comp.os.minix

Subject: Re: LINUX is obsolete

Date: 29 Jan 92 23:14:26 GMT

Organization: University of Helsinki

Well, with a subject like this, I’m afraid I’ll have to reply.

Apologies to minix-users who have heard enough about linux anyway. I’d

like to be able to just “ignore the bait”, but … Time for some

serious flamefesting!

In article <12595@star.cs.vu.nl> ast@cs.vu.nl (Andy Tanenbaum) writes:

>

>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 have a 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 senate hearings being televised live on CNN. My real

>job is a professor and researcher in the area of operating systems.

You use this as an excuse for the limitations of minix? Sorry, but you

loose: I’ve got more excuses than you have, and linux still beats the

pants of minix in almost all areas. Not to mention the fact that most

of the good code for PC minix seems to have been written by Bruce Evans.

Read Also: OPEN SOURCE HARDWARE COULD DEFEND AGAINST THE NEXT GENERATION OF HACKING

Re 1: you doing minix as a hobby – look at who makes money off minix,

and who gives linux out for free. Then talk about hobbies. Make minix

freely available, and one of my biggest gripes with it will disappear.

Linux has very much been a hobby (but a serious one: the best type) for

me: I get no money for it, and it’s not even part of any of my studies

in the university. I’ve done it all on my own time, and on my own

machine.

Re 2: your job is being a professor and researcher: That’s one hell of a

good excuse for some of the brain-damages of minix. I can only hope (and

assume) that Amoeba doesn’t suck like minix does.

>1. MICROKERNEL VS MONOLITHIC SYSTEM

True, linux is monolithic, and I agree that microkernels are nicer. With

a less argumentative subject, I’d probably have agreed with most of what

you said. From a theoretical (and aesthetical) standpoint linux looses.

If the GNU kernel had been ready last spring, I’d not have bothered to

even start my project: the fact is that it wasn’t and still isn’t. Linux

wins heavily on points of being available now.

> MINIX is a microkernel-based system. [deleted, but not so that you

> miss the point ] LINUX is a monolithic style system.

If this was the only criterion for the “goodness” of a kernel, you’d be

right. What you don’t mention is that minix doesn’t do the micro-kernel

thing very well, and has problems with real multitasking (in the

kernel). If I had made an OS that had problems with a multithreading

filesystem, I wouldn’t be so fast to condemn others: in fact, I’d do my

damndest to make others forget about the fiasco.

[ yes, I know there are multithreading hacks for minix, but they are

hacks, and bruce evans tells me there are lots of race conditions ]

>2. PORTABILITY

“Portability is for people who cannot write new programs”

-me, right now (with tongue in cheek)

The fact is that linux is more portable than minix. What? I hear you

say. It’s true – but not in the sense that ast means: I made linux as

conformant to standards as I knew how (without having any POSIX standard

in front of me). Porting things to linux is generally /much/ easier

than porting them to minix.

I agree that portability is a good thing: but only where it actually has

some meaning. There is no idea in trying to make an operating system

overly portable: adhering to a portable API is good enough. The very

/idea/ of an operating system is to use the hardware features, and hide

them behind a layer of high-level calls. That is exactly what linux

does: it just uses a bigger subset of the 386 features than other

kernels seem to do. Of course this makes the kernel proper unportable,

but it also makes for a /much/ simpler design. An acceptable trade-off,

and one that made linux possible in the first place.

I also agree that linux takes the non-portability to an extreme: I got

my 386 last January, and linux was partly a project to teach me about

it. Many things should have been done more portably if it would have

been a real project. I’m not making overly many excuses about it

though: it was a design decision, and last april when I started the

thing, I didn’t think anybody would actually want to use it. I’m happy

to report I was wrong, and as my source is freely available, anybody is

free to try to port it, even though it won’t be easy.

Linus

PS. I apologise for sometimes sounding too harsh: minix is nice enough

if you have nothing else. Amoeba might be nice if you have 5-10 spare

386’s lying around, but I certainly don’t. I don’t usually get into

flames, but I’m touchy when it comes to linux 🙂