Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cs.dal.ca!ug.cs.dal.ca!hart
From: hart@ug.cs.dal.ca (Todd Darrell Raymond Hart)
Newsgroups: comp.sys.amiga
Subject: Re: Format Error question(s) & Testimonial
Keywords: format, error, question
Message-ID: <1990Mar20.064147.1589@ug.cs.dal.ca>
Date: 20 Mar 90 06:41:47 GMT
References: <13211@burdvax.PRC.Unisys.COM>
Reply-To: hart@ug.cs.dal.ca.UUCP (Todd Darrell Raymond Hart)
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Lines: 44

>	A couple of times now, i've gotten errors while formatting a
> floppy.  since I get disks for 0.49 each, i don't mind tossing them,
> since it wouldn't be worth the effort to return them for a free
> replacement.
>
> Now the question:
>	is there a way to use disks with an error? M*-DOS is able to mark
> bad sectors, and was wondering if AmigaDOS would do the same.
>
> [REST DELETED...]
>
> Ralph

Well Ralph AmigaDOS does things in a slightly different way...when data is
written to the disk, the individual sector is *NOT* overwritten like in MS-DOS.
Instead AmigaDOS does things on a track by track basis.  The disk head moves
to the track the sector is in and writes out the entire track at once, it does
not bother to check to see what use to be there.  All sectors are written
back to the disk at the same time.  Therefore after each write to the disk
all data is together in one chunk with a single gap, and not necessarily at
the same place on the disk.  So one write may be fine and the next shows an
error.  An article in Amiga Transactor (Vol3, Iss1) gives an excellent
description of the encoding schemes used by disk drives and how they work.
To quote them:

	When you write to an Amiga floppy, the drive heads are given
	a track number to which they can write.  They then move
	immediately to the assigned track and begin writing.  They do not
	wait for a sync mark, nor do they look for a particular sector,
	and they are not likely to write on the same part of the track
	that was used before.

So that makes it kinda hard to mark a sector as bad as they are only a
logical representation of the data on the disk, not physical (one like
in MS-DOS).  As for your question of the Hard Disk, I don't know as I don't
have one yet (only a 500 with a single drive, but hopefully not for long
though) so I haven't bothered to really look into their inards other than
performance.
							-Todd
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__  ///  The AMIGA, not just another pretty face...                         |
\\\///                                  Todd D R Hart -- hart@ug.cs.dal.cs  |
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