Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!rosie!sstreep
From: sstreep@next.com (Sam Streeper)
Newsgroups: comp.sys.atari.st
Subject: Re: Help with ST <-> NeXT disk swapping
Keywords: NeXT, Atari, ST, DOS format, disk
Message-ID: <410@rosie.NeXT.COM>
Date: 23 Mar 91 21:20:26 GMT
References: <1991Mar22.211223.15978@wuphys.wustl.edu>
Sender: news@NeXT.COM
Distribution: usa
Organization: Next Computer, Inc.
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In article <1991Mar22.211223.15978@wuphys.wustl.edu> petcher@wuphys.UUCP (Donald N. Petcher) writes:
>I myself have a NeXTstation, and an Atari ST, and when I format an IBM 
>compatible 720K MS-DOS disk on the Atari, the NeXT seems to have no 
>problem reading it. However, if I write anything on the disk with the 
>NeXT, and then try to get the Atari to read it, it always acts as if the 
>disk is damaged and the files are unreadable. I have been able to get 
>the Atari to read a couple of small files but that is all.

This is my experience too.  IBM compatible formatted disks from the 
Atari read fine on the nextstation, but going the other way is
problematic, and reads fail if the file spans more than about 3 sectors.
Here is my guess as to the problem:

When you write 720K disks on the atari, you write the sectors as
comparatively strong, fat tracks.  A single data track is fairly
wide, so a single track looks something like this after formatting
with 0xE5 as a formatting value:

	E5  E5  E5  E5  E5  E5  E5  E5  E5  E5
	E5  E5  E5  E5  E5  E5  E5  E5  E5  E5

The NeXT drive by default writes tracks twice as dense and half as narrow,
which is how it offers 4x the data capacity.  When it senses that it is
writing a 720K dos disk, it writes the data at the same data density and
track spacing of a DOS disk, but the tracks are still comparatively
narrow.  Thus, on a clean disk, the NeXT might lay down a track like
this:

	FF  FF  FF  FF  FF  FF  FF  FF  FF  FF

The NeXT has no problem reading this, but I suspect that the track is
too narrow (and perhaps weak) for the Atari drive, which only correctly
reads it sporadically.  The worst case scenario could occur when fat
tracks are written (as in formatting) on the Atari and overwritten by
the NeXT.  In this case, a single track might look like this:

	E5  E5  E5  E5  E5  E5  E5  E5  E5  E5
	FF  FF  FF  FF  FF  FF  FF  FF  FF  FF

This track would be correctly read by the NeXT, but the Atari drive head
simultaneously reads both tracks with predictably poor results.

This situation may apply to 720K IBM machines as well, but I don't have
any experience there.  For what it's worth, NeXT written disks read
perfectly on a Compaq 386 with a 1.44 meg drive.  Also, this problem
could affect Atari machines differently; when I worked at an Atari service
center, we counted _nine_ (!) different suppliers of floppy drives, with
widely varying degrees of quality.


>I would like to know if this is similar to others' experiences or if it
>is peculiar to my system. Also is there a way to format an IBM
>compatible disk using the NeXT? 

Use /NextAdmin/BuildDOS to format the disk.

-sam
(sam_s@NeXT.com)
Opinions are not those of my employer, and could be totally wrong, besides...