Path: utzoo!attcan!utgpu!watmath!watdragon!rose!ccplumb
From: ccplumb@rose.waterloo.edu (Colin Plumb)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Boot Block
Keywords: Boot Block
Message-ID: <17605@watdragon.waterloo.edu>
Date: 27 Oct 89 16:59:53 GMT
References: <582@milton.acs.washington.edu>
Sender: daemon@watdragon.waterloo.edu
Reply-To: ccplumb@rose.waterloo.edu (Colin Plumb)
Organization: U. of Waterloo, Ontario
Lines: 31

In article <582@milton.acs.washington.edu> zeno@milton.acs.washington.edu (Sean Lamont) writes:
> I am kind of curious how the non-dos format disks work, and how the
> boot block works into this.  If the disk is nonstandard, how does the
> machine read it?  In fact, how does it manage to read the boot block if
> it has not had the read-format defined?  How would I go about writing my
> own format of data on the disk?

There are two layers of formatting imposed on a disk.  One divides it
into sectors, and is handled by the SCSI controller, trackdisk.device,
or whatever.  On top of that, AmigaDOS places a directory and file
structure.  It is possible to change either level without affecting
the other, although a change to the lower level must still maintain
the illusion of same-sized sectors.  If you want to write something using
the trackdisk.device but not the DOS file system, go right ahead.
ACTION_DISABLE the file system, if any, open the trackdisk.device or
whatever, and stomp away.  Try to be careful not to let DOS see the result,
as it might get confused.

> Where is the boot block located, as a physical track/surface (for use
> by a disk editor to look at it)  What does it do?  Does anybody have a
> disassembly of it?

On a floppy, blocks 0 and 1, which are located in sectors 0 and 1, track 0,
side 0.

The standard boot block (written by install) basically just fires up an
initial CLI and starts it running the startup-sequence.  I think it also
initialises Intuition a bit, but I'm pretty sure Intuition is started
by kickstart before loading the boot blocks.
-- 
	-Colin Plumb