Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!ginosko!cs.utexas.edu!uunet!portal!atari!apratt
From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: 82 tracks, twister, etc.
Message-ID: <1746@atari.UUCP>
Date: 25 Oct 89 17:07:10 GMT
References: <1295@mrsvr.UUCP>
Organization: Atari Corp., Sunnyvale CA
Lines: 33

krieg@jupiter.uucp (Andrew Krieg) writes:

>I have a few questions about disks and disk formatting for the ST.
>	1) [What is Twister format?]
>	2) [Why 82 tracks?]
>	3) [Are there any 1.4M drives out there?]

"Twisted" disks have sectors on successive tracks offset from one
another.  Instead of always starting sector 1 at the index mark, they
start sector 1 there on track 0, sector 3 on track 1, sector 5 on track
2, and so on.  This makes disk I/O faster, because there are only two
sectors of latency between reading sector 9 from track 0 and sector 1
of track 1, instead of 9 sectors of latency waiting for the whole disk
to spin around.

You get "Twisted" disks any time you format a disk from the Desktop
using Mega TOS or any newer TOS.  Once the disk is formatted it will be
fast no matter where you use it.

Atari disk drives are only guaranteed to handle 80 tracks.  Some people
have discovered that some drives can actually access 82 tracks, so they
have written formatters which will format 82 tracks.  This is not
recommended, and you can actually damage your disk drive by telling it
to seek so far that it bangs into something.  The Desktop format
operation will only format 80 tracks.

I am not aware of any 1.4M drives available for the ST.  I know you
couldn't just plug one in: they get 1.4M by doubling the data rate, and
the controller inside the ST couldn't handle it.

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt