Re: A2 Breakthru!

[mjmahon@aol.com (Michael J. Mahon)]

In article <2182312.LILEIXBU@news.telusplanet.net>, Simon Williams
<*email*@*luddite.ca*> writes:

>I suppose now would be the time for someone to explain exactly how this
>program [DiskDup+] differs from Disk Copy... Mr Mahon?  ;-)

I must admit to being quite intrigued by this result.

As far as I can remember, no one ever discovered exactly _why_ the
newer Macs didn't ("couldn't" isn't right anymore ;-) write A2-compatible
800K disks.  The usual hypothesis was that the new controller didn't
do the right thing on writing, but I don't recall any confirmation...it
now appears that the new disk formatting software may be the issue.

It would be very interesting to examine the nibble structure of a
DiskCopy-written disk and compare it with a DiskDup+ disk.

I suspect, now, that the Mac low-level format--which has always
had extra bits in it that the Apple II does not use--may have changed
subtly in a way that interferes with A2 compatibility.  DiskCopy just
writes to disks pre-formatted by Mac system software, while DiskDup+
evidently writes entire tracks, formatting as it writes.  If it writes the
low level format in the old way (not having been recently updated),
then it may not be subject to the (postulated) formatting-incompatiblity
introduced with the PowerMacs (and perhaps not affecting all types
of 3.5" drives).

Could someone (Paul?) who has made DiskCopy disks (that don't
work) and DiskDup+ disks (that do), please take a look at the nibbles
in, say, Copy II+, and see if there's a visible difference?

-michael

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