Note: The following text was written by Linus on July 31 1992. It is a
   collection of various artifacts from the period in which Linux first
   began to take shape.
   
   This is just a sentimental journey into some of the first posts
   concerning linux, so you can happily press 'n' now if you actually
   thought you'd get anything technical.

  From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
  Newsgroups: comp.os.minix
  Subject: Gcc-1.40 and a posix-question
  Message-ID:
  Date: 3 Jul 91 10:00:50 GMT

  Hello netlanders,

  Due to a project I'm working on (in minix), I'm interested in the posix
  standard definition. Could somebody please point me to a (preferably)
  machine-readable format of the latest posix rules? Ftp-sites would be
  nice.

   The project was obviously linux, so by July 3rd I had started to think
   about actual user-level things: some of the device drivers were ready,
   and the harddisk actually worked. Not too much else.

  As an aside for all using gcc on minix - [ deleted ]

   Just a success-report on porting gcc-1.40 to minix using the 1.37
   version made by Alan W Black & co.

                Linus Torvalds          torvalds@kruuna.helsinki.fi

  PS. Could someone please try to finger me from overseas, as I've
  installed a "changing .plan" (made by your's truly), and I'm not certain
  it works from outside? It should report a new .plan every time.

   So I was clueless - had just learned about named pipes. Sue me. This
   part of the post got a lot more response than the actual POSIX query,
   but the query did lure out arl from the woodwork, and we mailed around
   for a bit, resulting in the Linux subdirectory on nic.funet.fi.
   
   Then, almost two months later, I actually had something working: I
   made sources for version 0.01 available on nic sometimes around this
   time. 0.01 sources weren't actually runnable: they were just a token
   gesture to arl who had probably started to despair about ever getting
   anything. This next post must have been from just a couple of weeks
   before that release.

  From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
  Newsgroups: comp.os.minix
  Subject: What would you like to see most in minix?
  Summary: small poll for my new operating system
  Message-ID:
  Date: 25 Aug 91 20:57:08 GMT
  Organization: University of Helsinki


  Hello everybody out there using minix -

  I'm doing a (free) operating system (just a hobby, won't be big and
  professional like gnu) for 386(486) AT clones.  This has been brewing
  since april, and is starting to get ready.  I'd like any feedback on
  things people like/dislike in minix, as my OS resembles it somewhat
  (same physical layout of the file-system (due to practical reasons)
  among other things).

  I've currently ported bash(1.08) and gcc(1.40), and things seem to work.
  This implies that I'll get something practical within a few months, and
  I'd like to know what features most people would want.  Any suggestions
  are welcome, but I won't promise I'll implement them :-)

                Linus (torvalds@kruuna.helsinki.fi)

  PS.  Yes - it's free of any minix code, and it has a multi-threaded fs.
  It is NOT protable (uses 386 task switching etc), and it probably never
  will support anything other than AT-harddisks, as that's all I have :-(.

   Judging from the post, 0.01 wasn't actually out yet, but it's close.
   I'd guess the first version went out in the middle of September -91. I
   got some responses to this (most by mail, which I haven't saved), and
   I even got a few mails asking to be beta-testers for linux. After that
   just a few general answers to quesions on the net:

  From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
  Newsgroups: comp.os.minix
  Subject: Re: What would you like to see most in minix?
  Summary: yes - it's nonportable
  Message-ID:
  Date: 26 Aug 91 11:06:02 GMT
  Organization: University of Helsinki

  In article  jkp@cs.HUT.FI (Jyrki Kuoppala) writes:
  >> [re: my post about my new OS]
  >
  >Tell us more!  Does it need a MMU?

  Yes, it needs a MMU (sorry everybody), and it specifically needs a
  386/486 MMU (see later).

  >
  >>PS.  Yes - it's free of any minix code, and it has a multi-threaded fs.
  >>It is NOT protable (uses 386 task switching etc)
  >
  >How much of it is in C?  What difficulties will there be in porting?
  >Nobody will believe you about non-portability ;-), and I for one would
  >like to port it to my Amiga (Mach needs a MMU and Minix is not free).

  Simply, I'd say that porting is impossible.  It's mostly in C, but most
  people wouldn't call what I write C.  It uses every conceivable feature
  of the 386 I could find, as it was also a project to teach me about the
  386.  As already mentioned, it uses a MMU, for both paging (not to disk
  yet) and segmentation. It's the segmentation that makes it REALLY 386
  dependent (every task has a 64Mb segment for code & data - max 64 tasks
  in 4Gb. Anybody who needs more than 64Mb/task - tough cookies).

  It also uses every feature of gcc I could find, specifically the __asm__
  directive, so that I wouldn't need so much assembly language objects.
  Some of my "C"-files (specifically mm.c) are almost as much assembler as
  C. It would be "interesting" even to port it to another compiler (though
  why anybody would want to use anything other than gcc is a mystery).

   Note: linux has in fact gotten more portable with newer versions:
   there was a lot more assembly in the early versions. It has in fact
   been ported to other architectures by now.

  Unlike minix, I also happen to LIKE interrupts, so interrupts are
  handled without trying to hide the reason behind them (I especially like
  my hard-disk-driver.  Anybody else make interrupts drive a state-
  machine?).  All in all it's a porters nightmare.

  >As for the features; well, pseudo ttys, BSD sockets, user-mode
  >filesystems (so I can say cat /dev/tcp/kruuna.helsinki.fi/finger),
  >window size in the tty structure, system calls capable of supporting
  >POSIX.1.  Oh, and bsd-style long file names.

  Most of these seem possible (the tty structure already has stubs for
  window size), except maybe for the user-mode filesystems. As to POSIX,
  I'd be delighted to have it, but posix wants money for their papers, so
  that's not currently an option. In any case these are things that won't
  be supported for some time yet (first I'll make it a simple minix-
  lookalike, keyword SIMPLE).

                Linus (torvalds@kruuna.helsinki.fi)

  PS. To make things really clear - yes I can run gcc on it, and bash, and
  most of the gnu [bin/file]utilities, but it's not very debugged, and the
  library is really minimal. It doesn't even support floppy-disks yet. It
  won't be ready for distribution for a couple of months. Even then it
  probably won't be able to do much more than minix, and much less in some
  respects. It will be free though (probably under gnu-license or similar).

   Well, obviously something worked on my machine: I doubt I had yet
   gotten gcc to compile itself under linux (or I would have been too
   proud of it not to mention it). Still before any release-date.
   
   Then, October 5th, I seem to have released 0.02. As I already
   mentioned, 0.01 didn't actually come with any binaries: it was just
   source code for people interested in what linux looked like. Note the
   lack of announcement for 0.01: I wasn't too proud of it, so I think I
   only sent a note to everybody who had shown interest.

  From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
  Newsgroups: comp.os.minix
  Subject: Free minix-like kernel sources for 386-AT
  Message-ID:
  Date: 5 Oct 91 05:41:06 GMT
  Organization: University of Helsinki

  Do you pine for the nice days of minix-1.1, when men were men and wrote
  their own device drivers? Are you without a nice project and just dying
  to cut your teeth on a OS you can try to modify for your needs? Are you
  finding it frustrating when everything works on minix? No more all-
  nighters to get a nifty program working? Then this post might be just
  for you :-)

  As I mentioned a month(?) ago, I'm working on a free version of a
  minix-lookalike for AT-386 computers.  It has finally reached the stage
  where it's even usable (though may not be depending on what you want),
  and I am willing to put out the sources for wider distribution.  It is
  just version 0.02 (+1 (very small) patch already), but I've successfully
  run bash/gcc/gnu-make/gnu-sed/compress etc under it.

  Sources for this pet project of mine can be found at nic.funet.fi
  (128.214.6.100) in the directory /pub/OS/Linux.  The directory also
  contains some README-file and a couple of binaries to work under linux
  (bash, update and gcc, what more can you ask for :-).  Full kernel
  source is provided, as no minix code has been used.  Library sources are
  only partially free, so that cannot be distributed currently.  The
  system is able to compile "as-is" and has been known to work.  Heh.
  Sources to the binaries (bash and gcc) can be found at the same place in
  /pub/gnu.

  ALERT! WARNING! NOTE! These sources still need minix-386 to be compiled
  (and gcc-1.40, possibly 1.37.1, haven't tested), and you need minix to
  set it up if you want to run it, so it is not yet a standalone system
  for those of you without minix. I'm working on it. You also need to be
  something of a hacker to set it up (?), so for those hoping for an
  alternative to minix-386, please ignore me. It is currently meant for
  hackers interested in operating systems and 386's with access to minix.

  The system needs an AT-compatible harddisk (IDE is fine) and EGA/VGA. If
  you are still interested, please ftp the README/RELNOTES, and/or mail me
  for additional info.

  I can (well, almost) hear you asking yourselves "why?".  Hurd will be
  out in a year (or two, or next month, who knows), and I've already got
  minix.  This is a program for hackers by a hacker.  I've enjouyed doing
  it, and somebody might enjoy looking at it and even modifying it for
  their own needs.  It is still small enough to understand, use and
  modify, and I'm looking forward to any comments you might have.

  I'm also interested in hearing from anybody who has written any of the
  utilities/library functions for minix. If your efforts are freely
  distributable (under copyright or even public domain), I'd like to hear
  from you, so I can add them to the system. I'm using Earl Chews estdio
  right now (thanks for a nice and working system Earl), and similar works
  will be very wellcome. Your (C)'s will of course be left intact. Drop me
  a line if you are willing to let me use your code.

                Linus

  PS. to PHIL NELSON! I'm unable to get through to you, and keep getting
  "forward error - strawberry unknown domain" or something.

   Well, it doesn't sound like much of a system, does it? It did work,
   and some people even tried it out. There were several bad bugs (and
   there was no floppy-driver, no VM, no nothing), and 0.02 wasn't really
   very useable.
   
   0.03 got released shortly thereafter (max 2-3 weeks was the time
   between releases even back then), and 0.03 was pretty useable. The
   next version was numbered 0.10, as things actually started to work
   pretty well. The next post gives some idea of what had happened in two
   months more...

  From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
  Newsgroups: comp.os.minix
  Subject: Re: Status of LINUX?
  Summary: Still in beta
  Message-ID:
  Date: 19 Dec 91 23:35:45 GMT
  Organization: University of Helsinki

  In article  miquels@maestro.htsa.aha.nl (Miquel van Smoorenburg) writes:
  >Hello *,
  >     I know some people are working on a FREE O/S for the 386/486,
  >under the name Linux. I checked nic.funet.fi now and then, to see what was
  >happening. However, for the time being I am without FTP access so I don't
  >know what is going on at the moment. Could someone please inform me about it
?
  >It's maybe best to follow up to this article, as I think that there are
  >a lot of potential interested people reading this group. Note, that I don't
  >really *have* a >= 386, but I'm sure in time I will.

  Linux is still in beta (although available for brave souls by ftp), and
  has reached the version 0.11.  It's still not as comprehensive as
  386-minix, but better in some respects.  The "Linux info-sheet" should
  be posted here some day by the person that keeps that up to date.  In
  the meantime, I'll give some small pointers.

  First the bad news:

        - Still no SCSI: people are working on that, but no date yet.
          Thus you need a AT-interface disk (I have one report that it
          works on an EISA 486 with a SCSI disk that emulates the
          AT-interface, but that's more of a fluke than anything else:
          ISA+AT-disk is currently the hardware setup)

   As you can see, 0.11 had already a small following. It wasn't much,
   but it did work.

        - still no init/login: you get into bash as root upon bootup.

   That was still standard in the next release.

        - although I have a somewhat working VM (paging to disk), it's not
          ready yet.  Thus linux needs at least 4M to be able to run the
          GNU binaries (especially gcc).  It boots up in 2M, but you
          cannot compile.

   I actually released a 0.11+VM version just before Christmas -91: I
   didn't need it myself, but people were trying to compile the kernel in
   2MB and failing, so I had to implement it. The 0.11+VM version was
   available only to a small number of people that wanted to test it out:
   I'm still surprised it worked as well as it did.

        - minix still has a lot more users: better support.

        - it hasn't got years of testing by thousands of people, so there
          are probably quite a few bugs yet.

  Then for the good things..

        - It's free (copyright by me, but freely distributable under a
          very lenient copyright)

   The early copyright was in fact much more restrictive than the GNU
   copyleft: I didn't allow any money at all to change hands due to
   linux. That changed with 0.12.

        - it's fun to hack on.

        - /real/ multithreading filesystem.

        - uses the 386-features.  Thus locked into the 386/486 family, but
          it makes things clearer when you don't have to cater to other
          chips.

        - a lot more... read my .plan.

  /I/ think it's better than minix, but I'm a bit prejudiced.  It will
  never be the kind of professional OS that Hurd will be (in the next
  century or so :), but it's a nice learning tool (even more so than
  minix, IMHO), and it was/is fun working on it.

                Linus (torvalds@kruuna.helsinki.fi)

  ---- my .plan --------------------------
        Free UNIX for the 386 - coming 4QR 91 or 1QR 92.

  The current version of linux is 0.11 - it has most things a unix kernel
  needs, and will probably be released as 1.0 as soon as it gets a little
  more testing, and we can get a init/login going. Currently you get
  dumped into a shell as root upon bootup.

  Linux can be gotten by anonymous ftp from 'nic.funet.fi' (128.214.6.100)
  in the directory '/pub/OS/Linux'.  The same directory also contains some
  binary files to run under Linux.  Currently gcc, bash, update, uemacs,
  tar, make and fileutils.  Several people have gotten a running system,
  but it's still a hackers kernel.

  Linux still requires a AT-compatible disk to be useful: people are
  working on a SCSI-driver, but I don't know when it will be ready.

  There are now a couple of other sites containing linux, as people have
  had difficulties with connecting to nic. The sites are:
        Tupac-Amaru.Informatik.RWTH-Aachen.DE (137.226.112.31):
                directory /pub/msdos/replace
        tsx-11.mit.edu (18.172.1.2):
                directory /pub/linux

  There is also a mailing list set up 'Linux-activists@niksula.hut.fi'.
  To join, mail a request to 'Linux-activists-request@niksula.hut.fi'.
  It's no use mailing me: I have no actual contact with the mailing-list
  (other than being on it, naturally).

  Mail me for more info:

                Linus (torvalds@kruuna.Helsinki.FI)

  0.11 has these new things:

  - demand loading
  - code/data sharing between unrelated processes
  - much better floppy drivers (they actually work mostly)
  - bug-corrections
  - support for Hercules/MDA/CGA/EGA/VGA
  - the console also beeps (WoW! Wonder-kernel :-)
  - mkfs/fsck/fdisk
  - US/German/French/Finnish keyboards
  - settable line-speeds for com1/2

   As you can see: 0.11 was actually stand-alone: I wrote the first
   mkfs/fsck/fdisk programs for it, so that you didn't need minix any
   more to set it up. Also, serial lines had been hard-coded to 2400bps,
   as that was all I had.

  Still lacking:
  - init/login
  - rename system call
  - named pipes
  - symbolic links

   Well, they are all there now: init/login didn't quite make it to 0.12,
   and rename() was implemented as a patch somewhere between 0.12 and
   0.95. Symlinks were in 0.95, but named pipes didn't make it until
   0.96.
   
   Note: The version number went directly from 0.12 to 0.95, as the
   follow-on to 0.12 was getting feature-full enough to deserve a number
   in the 0.90's

  0.12 will probably be out in January (15th or so), and will have:
  - POSIX job control (by tytso)
  - VM (paging to disk)
  - Minor corrections

   Actually, 0.12 was out January 5th, and contained major corrections.
   It was in fact a very stable kernel: it worked on a lot of new
   hardware, and there was no need for patches for a long time. 0.12 was
   also the kernel that "made it": that's when linux started to spread a
   lot faster. Earlier kernel releases were very much only for hackers:
   0.12 actually worked quite well.
   
   
   
   Note: The following document is a reply by Linus Torvalds, creator of
   Linux, in which he talks about his experiences in the early stages of
   Linux development

To: Linux-Activists@BLOOM-PICAYUNE.MIT.EDU
From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
Subject: Re: Writing an OS - questions !!
Date: 5 May 92 07:58:17 GMT

In article  nani@td2cad.intel.com (V. Narayanan) writes:

 Hi folks,
         For quite some time this "novice" has been wondering as to how one goe
s
 about the task of writing an OS from "scratch".  So here are some questions,
 and I would appreciate if you could take time to answer 'em.

Well, I see someone else already answered, but I thought I'd take on the
linux-specific parts.  Just my personal experiences, and I don't know
how normal those are.

 1) How would you typically debug the kernel during the development phase?

Depends on both the machine and how far you have gotten on the kernel:
on more simple systems it's generally easier to set up. Here's what I
had to do on a 386 in protected mode.

The worst part is starting off: after you have even a minimal system you
can use printf etc, but moving to protected mode on a 386 isn't fun,
especially if you at first don't know the architecture very well.  It's
distressingly easy to reboot the system at this stage: if the 386
notices something is wrong, it shuts down and reboots - you don't even
get a chance to see what's wrong.

Printf() isn't very useful - a reboot also clears the screen, and
anyway, you have to have access to video-mem, which might fail if your
segments are incorrect etc.  Don't even think about debuggers: no
debugger I know of can follow a 386 into protected mode.  A 386 emulator
might do the job, or some heavy hardware, but that isn't usually
feasible.

What I used was a simple killing-loop: I put in statements like

die:
        jmp die

at strategic places.  If it locked up, you were ok, if it rebooted, you
knew at least it happened before the die-loop.  Alternatively, you might
use the sound io ports for some sound-clues, but as I had no experience
with PC hardware, I didn't even use that.  I'm not saying this is the
only way: I didn't start off to write a kernel, I just wanted to explore
the 386 task-switching primitives etc, and that's how I started off (in
about April-91).

After you have a minimal system up and can use the screen for output, it
gets a bit easier, but that's when you have to enable interrupts. Bang,
instant reboot, and back to the old way. All in all, it took about 2
months for me to get all the 386 things pretty well sorted out so that I
no longer had to count on avoiding rebooting at once, and having the
basic things set up (paging, timer-interrupt and a simple task-switcher
to test out the segments etc).

 2) Can you test the kernel functionality by running it as a process on a
    different OS?  Wouldn't the OS(the development environment) generate
    exceptions in cases when the kernel (of the new OS) tries to modify
    'priviledged' registers?

Yes, it's generally possible for some things, but eg device drivers
usually have to be tested out on the bare machine.  I used minix to
develop linux, so I had no access to IO registers, interrupts etc.
Under DOS it would have been possible to get access to all these, but
then you don't have 32-bit mode.  Intel isn't that great - it would
probably have been much easier on a 68040 or similar.

So after getting a simple task-switcher (it switched between two
processes that printed AAAA...  and BBBB...  respectively by using the
timer-interrupt - Gods I was proud over that), I still had to continue
debugging basically by using printf.  The first thing written was the
keyboard driver: that's the reason it's still written completely in
assembler (I didn't dare move to C yet - I was still debugging at
about instruction-level).

After that I wrote the serial drivers, and voila, I had a simple
terminal program running (well, not that simple actually).  It was still
the same two processes (AAA..), but now they read and wrote to the
console/serial lines instead.  I had to reboot to get out of it all, but
it was a simple kernel.

After that is was plain sailing: hairy coding still, but I had some
devices, and debugging was easier.  I started using C at this stage, and
it certainly speeds up developement.  This is also when I start to get
serious about my megalomaniac ideas to make "a better minix that minix".
I was hoping I'd be able to recompile gcc under linux some day...

The harddisk driver was more of the same: this time the problems with
bad documentation started to crop up.  The PC may be the most used
architecture in the world right now, but that doesn't mean the docs are
any better: in fact I haven't seen /any/ book even mentioning the weird
386-387 coupling in an AT etc (Thanks Bruce).

After that, a small filesystem, and voila, you have a minimal unix.  Two
months for basic setups, but then only slightly longer until I had a
disk-driver (seriously buggy, but it happened to work on my machine) and
a small filesystem.  That was about when I made 0.01 available (late
august-91? Something like that): it wasn't pretty, it had no floppy
driver, and it couldn't do much anything.  I don't think anybody ever
compiled that version.  But by then I was hooked, and didn't want to
stop until I could chuck out minix.

 3) Would new linkers and loaders have to be written before you get a basic
    kernel running?

All versions up to about 0.11 were crosscompiled under minix386 - as
were the user programs.  I got bash and gcc eventually working under
0.02, and while a race-condition in the buffer-cache code prevented me
from recompiling gcc with itself, I was able to tackle smaller compiles.
0.03 (October?) was able to recompile gcc under itself, and I think
that's the first version that anybody else actually used.  Still no
floppies, but most of the basic things worked.

Afetr 0.03 I decided that the next version was actually useable (it was,
kind of, but boy is X under 0.96 more impressive), and I called the next
version 0.10 (November?).  It still had a rather serious bug in the
buffer-cache handling code, but after patching that, it was pretty ok.
0.11 (December) had the first floppy driver, and was the point where I
started doing linux developement under itself.  Quite as well, as I
trashed my minix386 partition by mistake when trying to autodial
/dev/hd2.

By that time others were actually using linux, and running out of
memory.  Especially sad was the fact that gcc wouldn't work on a 2MB
machine, and although c386 was ported, it didn't do everything gcc did,
and couldn't recompile the kernel.  So I had to implement disk-paging:
0.12 came out in January (?) and had paging by me as well as job control
by tytso (and other patches: pmacdona had started on VC's etc).  It was
the first release that started to have "non-essential" features, and
being partly written by others.  It was also the first release that
actually did many things better than minix, and by now people started to
really get interested.

Then it was 0.95 in March, bugfixes in April, and soon 0.96. It's
certainly been fun (and I trust will continue to be so) - reactions have
been mostly very positive, and you do learn a lot doing this type of
thing (on the other hand, your studies suffer in other respects :)