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From: bryce@COGSCI.BERKELEY.EDU (Bryce Nesbitt)
Newsgroups: comp.sys.amiga
Subject: Re: Reading MacDisks on Amiga
Message-ID: <8705091146.AA12102@cogsci.berkeley.edu>
Date: Sat, 9-May-87 07:46:30 EDT
Article-I.D.: cogsci.8705091146.AA12102
Posted: Sat May  9 07:46:30 1987
Date-Received: Sun, 10-May-87 04:01:12 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: bryce@cogsci.berkeley.edu (Bryce Nesbitt)
Organization: University of California, Berkeley
Lines: 34
Summary: How Mac+ drives read disks.

In article <2176@borealis.UUCP> barry@borealis.UUCP (Kenn Barry) writes:
><I've read several people who stated that, since the Mac drives spin
><at variable rates and the Amiga drives at fixed rates, that it was not
><possible to read Mac Disks with the Amiga drive.
>
>	Usual disclaimer ("I could be wrong"), but didn't Macs switch
>from variable speed to constant speed with the Mac+? I remember the
>funny "singing" noises the old Mac drives made, but not the new ones.
>
Old mac drives are multi-speed devices.  This allows more bits to be packed
on the outer tracks, since there is more physical space.  In the outer
zones old mac drives spin SLOWER, thus writing more information per degree
of arc.

[Editorial: despite this 'innovation' mac drives store pathetically little
 information (400k). Far too little considering the needs of the machine]

Mac+ drives run at a constant speed but the ELECTRONICS compensates and
read/writes data at a variable bit rate.  This is the same way that the
Commodore 2040/4040/8050/8250/1541/1571 drives work.

For the Amiga to *WRITE* mac disks if would need to have a set of bits
in paula to select bit rates to match those of the mac drives.  The Amiga
may be flexible enough as is to *READ* mac disks with some fancy software
that can compensate; interpolate and retry to extract good data from a
incompatible rate bit stream.

              /                      ====  ===   ==   ==
    //    /--|--\    **      |||      ==   =__=  = = = =
   //     |     (   |  ==    |||      ==   =  =  =  =  =
\\//      \_____/    **     / | \    ====  ===   =  =  = 

Me?  I like the    //        
                \\//  but the MAC II also has a lot going for it.