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From: tsarna@polar.bowdoin.edu (Tyler Sarna)
Newsgroups: comp.os.minix
Subject: Re: Amiga & Atari minix 1.5 questions
Message-ID: <42917@nigel.ee.udel.edu>
Date: 28 Jan 91 03:07:26 GMT
Sender: mmdf@ee.udel.edu
Lines: 72

In comp.os.minix, "Berry A.W. van Halderen (I88"
<halderen%FWI.UVA.NL@VM1.NoDak.EDU> writes:

> AmigaMinix does use the same kind of diskformat as STminix, so you can
> read, write, and execute (!? I though so) ST disks.

Yes, this is true.

> This is why AmigaMinix is kinda slow when accessing disks (the amiga
> diskdrive doesn't like to read and write IBM-formatted disks).

Not true! I beleive this to be a problem with the floppy driver
in minix - recent posts point to this.

Amiga floppy drives are physically the same as PC/ST drives -
unlike Mac drives. The difference between the native formats of
the PC/ST and the Amiga is due to software/controller issues.
AmigaDOS reads/writes whole tracks, which are broken into
sectors only logically. This is why the AmigaDOS driver is
called "trackdisk.device". They also use two different encoding
methods - I beleive the PC/ST uses GCR and the Amiga MFM.

There are two main side-effects of the Amiga native format:

1) More data can be stored on a disk: 880K for AmigaDOS versus
   720K for PC/ST and 800K for the MAC.
2) Most PC (I don't know about the ST) floppy controllers simply
   can't deal with the whole-track layout, which is why the
   PC/(ST ?) can't be made to read AmigaDOS disks.

On the other hand, the Amiga can be easily made to read and
write other disks, since the drive hardware is the same. There are
several approaches to this:

1) A program that reads/writes PC (or minix) disks, such as
   Dos-2-Dos (or minix transfer).
2) A new driver/filesystem, such as MSH or a commercial program
   whose name escapes me a the moment. With MSH, for example,
   you simply install a new new device-driver (messydisk.device)
   and a new filesystem handler (MessyFileSystem) [note: pokes
   at MS-DOS ("Messy-DOS") brain damage are the MSH author's,
   not my own :-)]. The user sets up the correct mounlist entry,
   and then does "mount msh:". From then on, device msh: acts
   just like any other amiga drive, except that it has "8.3"
   filename constraints.

As a sidenote, due to the lovely modular design of AmigaDOS, one
can use StandardFileSystem with messydisk.device to get an Amiga
filesystem on PC layout disks (which could presumably be read by
someone with a PC who wanted towrite a program to traverse the
Amiga filesystem). One can also use MessyFileSystem with
trackdisk.device to make MS-DOS disks which can't be read on an
MS-DOS machine, or with scsi.device for someone who wants a
MS-DOS filesystem hard drive. These are all pretty useless
ideas, but it's nice not to be limited.

What DOES sound like it might be useful is to use a PD handler
(I forget the name) which makes a raw stream device out of
trackdisk.device, allowing someone to, say, use tar and write to
the floppy as if it were a file. This handler allows and .device
to be used, so my idea is to use it with messydisk.device from
MSH and be able to exchange tar disks between AmigaDOS and
Minix. I haven't tried this yet, but if it works it would be far
superior than transfer. Another possibility is to write a
MinixFileSystem to use with messydisk.device, and have
transparent access to minix disks. It could even support file
links under AmigaDOS 2.0!

------///------------------------------------------------------------
     /// Tyler "Ty" Sarna            E-Mail: tsarna@polar.bowdoin.edu 
 \\\///       "The Electric Monk was a labour-saving device..."
--\XX/---------------------------------------------------------------