Von:Commodore Amiga (amiga@cs.vu.nl)
Betrifft:AmigaMINIX, some answers 
Newsgroups:comp.os.minix, comp.sys.amiga
Datum:1989-07-25 04:38:29 PST 




  Finally some answers about AmigaMINIX from the guys who ported it. We
hope that the following will clarify most of the darker areas around
AmigaMINIX.

  For those of you who don't know what AmigaMINIX is about: it's a UNIX
like operating system for you Amiga.  MINIX was originally written by
Andy Tanenbaum for the PC-family and later on ported to the Atari-ST by
Johan Stevenson and Jost Muller. Because the ST version is based on the
Motorola 68000 we decided to port this version to the Amiga.

  While porting MINIX to the Amiga we've tried to keep the main goal of
MINIX (education) in mind. This means we did not try to squeeze out every
bit of performance, especially not where this would harm the clarity of
the MINIX source code and/or structure. Another result of this goal is
that we decided not to use the usual Amiga disk format, but the PC (ST)
format instead. This way the AmigaMINIX and MINIX-ST file systems are 100%
compatible. Because MINIX doesn't use any dirty tricks, AmigaMINIX and
MINIX-ST binaries are also compatible; you can mount a MINIX-ST floppy on
AmigaMINIX and run all binaries. (Almost all, actually. Programs which do
use 'dirty tricks' as directly reading from /dev/ram to set the time-of-
day clock won't run properly of course!)

  Although we wanted to use the PC format for the AmigaMINIX floppies we
didn't want to fall asleep when loading mined for example. We tried to
optimize the floppy driver as much as we could be using a track cache for
each drive and only compute the CRCs (checksums) when necessary. (Computing
a CRC costs about 50 ms. This limits the transfer rate to 6.9 kb/sec. The
normal transfer rate under AmigaMINIX is 4 to 5 kb/sec) Since each track-
cache occupies about 14 kb of CHIPMEM, these buffers are dynamically
allocated for only those floppy drives that are actually connected.

  Apart from the PC format disks there's another remarkable 'thing' about
AmigaMINIX: it doesn't support hard disks. (sorry)  There are two main
reasons for this. In the first place there are several different hard
disks in use on Amiga's and we didn't want to write a driver for all of
them. Further, we didn't (and nobody in our neighborhood does) have a
hard disk to test our driver(s) on. If, however, hard disks are as common
in other places of the world as we're told, it shouldn't be long before
one of you will post a driver for your favorite hard disk.

  To sum up the most important specifications of AmigaMINIX:

 - AmigaMINIX boots from a normal AmigaDOS floppy (bootstrap) so
   it can easily steal (use) everything AmigaDOS knows about your
   Amiga. (Whether is's NTSC or PAL, how much memory do you have,
   what color the screen is, what keymap you use, etc.) After that
   it completely takes over your Amiga, and disables EXEC.

 - You can use ALL of the available RAM which is normally available
   under AmigaDOS, even if it's fragmented.

 - The floppy driver can read and write single and double sided 80-
   track floppies. (Also single sided for MINIX-ST compatibility.)
   Up to four drives can be connected.

 - The AmigaMINIX printer driver only supports the parallel (centro-
   nics) port.

 - The display driver use ANSI escape sequences and also provides
   limited access to the color registers.

  Some of you may wonder why we decided not to run AmigaMINIX under EXEC.
The main reason for this is that (at first) we thought that it wouldn't
run properly with the MINIX-ACK compiler. When we realized that this wasn't
such a big problem after all, the port was already half on its way. Another
reason is that we think that you should not run operating systems on top of
each other, if you want people to know what operating systems really is all
about. (Andy Tanenbaum once put it something like: "It's not writing a 15
page scheduler, but getting all the details right.")

  AmigaMINIX is currently being tested here on the VU and because we haven't
found a distributor yet and don't feel like posting 3 Mb (yet :-) it'll
probably be a while before you can use AmigaMINIX.

 -Steven Reiz & Raymond Michiels. (amiga@cs.vu.nl)


