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Path: utzoo!mnetor!seismo!rutgers!cbmvax!daveh
From: daveh@cbmvax.cbm.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Mac disks <--> Amiga disks
Message-ID: <1772@cbmvax.cbmvax.cbm.UUCP>
Date: Mon, 27-Apr-87 15:08:08 EDT
Article-I.D.: cbmvax.1772
Posted: Mon Apr 27 15:08:08 1987
Date-Received: Tue, 28-Apr-87 02:59:41 EDT
References: <3302@jade.BERKELEY.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 37

in article <3302@jade.BERKELEY.EDU>, spencer@eris.BERKELEY.EDU (Randy Spencer) says:
> So the question still stands:  Is there a program (for the Mac or the Amiga)
> that lets me read and write disks back and forth so that I don't have to 
> have a modem to transfer files from one machine to the other?

> Randy Spencer

There was a thread (here, or was it elsewhere) awhile back on the Amiga reading
of Mac disks.  It looks like at least some portions of a Mac disk could be
read, but perhaps not all of them.  The reason that anything could be read
from a Mac disk is due to the Amiga's decoding of the disk format under
software control (this is usually done by the blitter, but in this case you
might have to throw the CPU at it).  The reason you might not be able to 
read, and probably can't write, Mac disks is of course the speed change
that you mention (Mac's trick to fit 800K per DS disk).

The Amiga's trick for 880K+ per disk is based in the fact that it must,
by the nature of the floppy controller that's part of the Paula chip, write
or read an entire track at a time.  There are no individually accessed
physical sectors on an Amiga floppy, although logically you get 512 byte
blocks out of a track (11 per track per side on a standard Amiga 
floppy disk).  Traditional disk controllers must write a sector at a time,
and as a result of this they've got to leave a bit of room between
sectors so that a little bit of imprecision on the part of the drive
head won't clobber neighboring sectors.  Any machine, like a Mac, IBM,
or Atari ST that writes individual sectors would have trouble reading
or writing an Amiga disk.  Also, most of these machines have disk controllers
that implement the disk format in hardware, so even if they could accurately
read the Amiga floppys with their mechanicals, their silicon may not have a
clue as to what to do with the format.  Amiga's can read the standard 720K
format used by IBMs and Ataris with no trouble -- currently there are
programs that do this, there will probably be device drivers in the near
future.
-- 
Dave Haynie     Commodore-Amiga    Usenet: {ihnp4|caip|rutgers}!cbmvax!daveh
"The A2000 Guy"                    BIX   : hazy
	"These are the days of miracle and wonder" -P. Simon