Path: utzoo!mnetor!uunet!lll-winken!lll-tis!oodis01!uplherc!sp7040!obie!wes
From: wes@obie.UUCP (Barnacle Wes)
Newsgroups: comp.sys.atari.st
Subject: Re: Reading Mac disks?
Message-ID: <202@obie.UUCP>
Date: 1 May 88 18:35:57 GMT
References: <19880428185422.2.JRD@MOA.SCRC.Symbolics.COM>
Organization: Great Salt Lake Yacht Club, north branch
Lines: 32
Summary: Can't read Mac disks on the ST

In article <19880428185422.2.JRD@MOA.SCRC.Symbolics.COM>, jrd@STONY-BROOK.SCRC.SYMBOLICS.COM (John R. Dunning) writes:
> Does anyone know of a PD/Freeware way of reading and writing MAC disks
> on my ST?  I have access to a MAC II at work, and it'd be nice to be
> able to cart data back and forth on floppettes instead of via phone
> lines.  No, I DON'T want to run Magic Sac, I just want to read and write
> the disks.

You can't read Mac disks on the ST without hacking your disk drive and
controller some.  The Mac disk controller, the IWM (stands for
Integrated Woz Machine), uses a peculiar format.

Most floppies, and all hard disks (that I know of) use _constant angular
velocity_.  That means the disk always _spins_ at the same speed.  The
Mac, on the other hand, uses _constant linear velocity_ (or very near
constant) which means they speed up and slow down the rotational speed
to keep the part of the disk passing under the head moving at the same
speed _relative to the head_.

To be able to read and write Mac disks on the ST, you need a disk
drive and controller pair that supports this speeding up and slowing
down of the rotational speed.  Data Pacific sells one that goes with
the Magic Sac.  Other than that, you are pretty much out.

There is a program for the Amiga which will read/write Mac disks, or
so I'm told.  It will also read/write/format IBM PC and ST disks.  Got
a friend with an Amiga?  I might also be possible to write a Mac
program that can read/write ST disks - I don't know that much about
how programmable the IWM is.
-- 
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