Re: ProDos Disk Images

["Paul Grammens" <grammens@svn.net>]

Thanks, Roger, this saves me from trying DiskCopy 4.2 and an 800K drive.
I guess it just won't work.
-Paul

"Roger Johnstone" <rojaws@es.co.nz> wrote in message
3E2CE04D.2030401@es.co.nz">news:3E2CE04D.2030401@es.co.nz...
> Eric Smith wrote:
>
>  > mjmahon@aol.com (Michael J. Mahon) writes:
>  >
>  >> I expect that the Power Mac controller does not provide the
>  >> variable speed control voltage that the Superdrive floppy needs.
>  >> When you format a ProDOS (800K) disk, do you hear the drive
>  >> changing speeds?
>  >
>  >
>  > The Superdrive/FDHD does its own speed control.  The controller in
>  > recent Macs isn't capable of GCR.
>
> That's not right. All the Macs ever made with floppy drives can do GCR
> disks. You may be thinking of the recent Macs which don't have any
> floppy controller and rely on external USB drives. All the USB floppy
> drives available are only capable of MFM disks i.e. 720KB and 1.4MB.
>
> The issue is that Macs that have manual inject drives can make 800KB
> disks which work fine on another Mac, even an old ones with the auto
> inject drives, but the disks won't work in an Apple II.
>
> I think Michael is correct and that it is the drive controller Apple
> used. The original drives they used were variable speed so that they
> could get more data on the longer outside tracks by slowing down the
> disk's rotation. From what I understand, the manual inject drives are
> fixed speed drives like those used in most other computers. To vary the
> data rate they just changed the rate at which it was sent to the drive
> instead of changing the disk speed. This would have required a new
> controller chip, so the new chip coincided with the arrival of the new
> drive.
>
> The following is some more info I posted here a couple of years ago:
>
> --------
> There seem to be two problems here, one with Disk Copy and the other
> with the drives used in later Macs. Apple has a tech note at
> http://til.info.apple.com/techinfo.nsf/artnum/n30959 which mentions
> problems with the manual inject drives used in later Macs, when
> formatting Apple II disks.
>
> There is also a problem with Disk Copy, at least on my iMac running Mac
> OS 8.1. The iMacs don't have a floppy drive, but they do have all the
> hardware required to add one. I installed a D19 socket on the side of my
> iMac so I can plug in my IIgs 800KB drive, it works perfectly for Apple
> II or Mac 800KB disks.
>
> I did some experimenting today and found disks formatted from the Mac
> Finder and with the files copied onto it boot on the IIgs, but the same
> disk created with Disk Copy failed to boot past the *** UNABLE TO LOAD
> PRODOS *** stage, neither could the disk be cataloged (I/O error).
> Checking the disk with a verify program on the IIgs, it seems that
> every block gets an I/O error _except_ the boot block!
>
> (n.b.: remember that if you get the 'unable to load ProDOS' message it
> means that the disk did start to boot, since this message is an error
> reported by the program stored in the boot block itself, but the boot
> code could not find the ProDOS file on the disk, which will be the case
> if the rest of the disk can't be read)
>
> I put the drive back on the iMac and found that the Mac Finder could
> read the disk fine. I could even get Bernie to boot from it. The disk
> was also checked on a PowerBook 5300 and worked fine. The same disk
> created with Disk Copy on the PowerBook booted and ran on the IIgs.
>
> The problem with Disk Copy on my iMac is not the disk drive (real Apple
> II drive!) or the OS version (8.1, same as the PowerBook ) or the
> version of Disk Copy (latest 6.3.3 or older 4.2 produce same results).
> The only other thing I can think of is an incompatibilty between the
> iMac hardware and Disk Copy which causes the disks to be written in some
> funny format which a Mac can still read but an Apple II can't.
>
> --
> Roger Johnstone, Invercargill, New Zealand
>
> Apple II - FutureCop:LAPD - iMac Game Wizard
> http://homepages.ihug.co.nz/~rojaws/
> ________________________________________________________________________
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