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Using an USB external floppy drive, I've been able to use my Mac to back up files from a big box of 3.5 inch floppies (800K, HD 1.4MB). But I cannot even read my DS 1MB floppies using either the external USB drive, or the drive of a Classic II. (The Classic II kept freezing up). What kind of drive do I need, or what kind of legacy Mac would help?

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  • Does backup on a Mac use a different format to normal read/write. On Windows, backup disks can't be read normally but can be read by the restore program
    – cup
    Feb 2 at 13:27
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Many USB floppy drives will not read double-density (720 / 800 KB) disks at all. Most that can will only read 720 KB disks formatted for IBM PCs.

I am not aware of any standard USB 3.5" drives that can read the 800 KB double-density Mac format. They are unlikely to exist as 800 KB disks as used on the classic Macs use a proprietary on-disk format requiring variable speed drives.

If that is the kind of disk you want to read, any pre-iMac Mac with a standard 800 KB or 1.44 MB Macintosh drive should be able to read them. But classic Macs are about the only system that can easily read them.

With machine like your Classic II which has a 1.4 MB Mac drive, if you can get it running, you should be able to image the 800K disks using a utility like Disk Copy, then copy those image files to a 1.4 MB floppy. The USB drive should be able to read a 1.4 MB HD floppy. That will give you an exact copy of your disks, hopefully.

Another option would be to consider something like (with no particular endorsement) the Kryoflux, FluxEngine, Applesauce or similar. They do very low-level magnetic imaging of the disk's surface, and then use hefty modern software to reconstruct the bytes. But these are mostly hobbyist-level projects and would be somewhat involved, I think.

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    KryoFlux isn't hobbyist-level, and the GUI makes it easy to produce disk images from Mac floppies if you know what to pick in the format selector... but it's expensive and the choice of floppy drive to plug into it can still affect whether you get a successful read on some of the zones on your disk in my experience. (400K/800K disks are zoned CAV, where the disk is split into different zones with different intended spindle speeds.)
    – ssokolow
    Feb 2 at 5:05
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    Another option is an Amiga. Amiga's were popular back in the day as copy stations. The original DD Amiga drives, with the right software, could basically read and write anything, including Mac disks. Later HD drives were tricky. Original Commodore drives could do it too, except for the floppy drive in later A4000 machines. 3rd party HD drives usually could not. as they used the cheaper standard HD floppy drives for IBM compatibles. In other words: The same problem poster has with the USB HD drive.
    – Tonny
    Feb 2 at 10:18
  • @Tonny are you sure an Amiga can read anything, including Mac disks? I understood that it uses a standard Shugart-bus drive. Therefore it has a fixed rotation speed. So it'd need to be able to read and write at some really odd densities to hit all five of the Mac's speed zones, but I also understood that the drive controller has a fixed data rate.
    – Tommy
    Feb 2 at 20:37
  • @Tommy You are right about the speed, but the bit-timing was adjustable and you could read/write raw data from the floppy. That allows you to read/write special formats, including Mac and AtariST DS floppies. Amiga games used this a lot as copy protection as well. Floppies would intentionally have 1 or more tracks with weird formatting. That stymied the normal diskcopy tool, but specialized copy-tools (Eg. NibbleCopy, X-CopyPro, SuperDuper) had no problem. Trick was not to try to interpret the content. Just copy raw data between 2 drives with high enough bit-timing to get all the bits.
    – Tonny
    Feb 3 at 9:33

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