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Thread: Writing Mac 800kB disks

  1. #1
    Join Date
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    Default Writing Mac 800kB disks

    People might be interested to know that I've just merged in successful write support for those horrible 800kB disks to FluxEngine, my USB FDD interface project (tl;dr: it's essentially a very cheap and open source DIY Kryoflux or SuperCardPlus replacement). I can download a System 6 DiskCopy 4.2 image from MacintoshGarden, write it to a floppy, and then boot from it.

    If anyone's got one of the 800kB-only machines like a Mac Plus, I'd be really interested to know if it works there. I have very limited hardware for testing (one beaten-up PowerBook 150).

    http://cowlark.com/fluxengine/

  2. #2

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    Quote Originally Posted by hjalfi View Post
    People might be interested to know that I've just merged in successful write support for those horrible 800kB disks to FluxEngine, my USB FDD interface project (tl;dr: it's essentially a very cheap and open source DIY Kryoflux or SuperCardPlus replacement). I can download a System 6 DiskCopy 4.2 image from MacintoshGarden, write it to a floppy, and then boot from it.

    If anyone's got one of the 800kB-only machines like a Mac Plus, I'd be really interested to know if it works there. I have very limited hardware for testing (one beaten-up PowerBook 150).

    http://cowlark.com/fluxengine/
    Are you asking for someone to volunteer receiving a floppy disk from you and testing it on their machine to ensure it works ?

  3. #3

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    Quote Originally Posted by hjalfi View Post
    I can download a System 6 DiskCopy 4.2 image from MacintoshGarden, write it to a floppy, and then boot from it.
    Just for the record: I can write 800k DiskCopy images to a 1.44MB disk using WinImage and a USB floppy drive and my Mac Classic will boot from them, too. Doesn't say much about whether or not a Mac with a real 800k drive can boot from them. Don't own one for testing, sadly.

  4. #4
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    Yeah, you can put a 800kB filesystem image on a 1440kB MFM disk and it'll work just fine, if you have a Mac which can read them. Of course, if you do that, then you don't get to hear the lovely tunes as the machine boots and the CLV drive spins up and down.

  5. Default

    Quote Originally Posted by Timo W. View Post
    Just for the record: I can write 800k DiskCopy images to a 1.44MB disk using WinImage and a USB floppy drive and my Mac Classic will boot from them, too. Doesn't say much about whether or not a Mac with a real 800k drive can boot from them.
    I wouldn't count on it. You did the floppy equivalent of partitioning a hard disk, and leaving some of the total capacity unused.

  6. #6
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    Default

    I wasn't aware WinImage would do that, but either way that is the same as converting to a 1.44mb MFM formatted disk, even if it does not resize to add the extra space. Unless I am mistaken, That trick would only work with HFS volumes, not MFS disks.

    So the resulting disks written by Winimage/USB drives will NOT be readable on any Macintosh that has only a 400k/800k floppy drive.

    Real 400k/800k Macintosh disks are very tricky because they use both CGR encoding and variable bitrates on different tracks.

    IBM PC style floppy controllers can not read/write this format at all. Flux-level devices that read/write this format using a PC style floppy drive must change the bitrate going to/from the drive since IBM PC style drives always spin at the same speed. (On a Macintosh, the bitrate at the controller is always the same, but the disk spins at different speeds)

    Note that not all standard PC 1.44mb floppy drives can deal with GCR/variable bit rates. Electronic filters designed to remove random noise from MFM signals will treat GCR/VBR as "noise" and filter it out. I've found that typically Teac and Toshiba 1.44mb drives are usually the best.

  7. #7
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    Most Mac Performas can handle both the 800K (some, the 400K) GCR floppies, as well as the 1.44M MFM floppies. Not so the early 68K Macs.

    An IBM PC with a Deluxe Option Board installed can read and write the GCR floppies and comes with utilities to understand the file system.

  8. #8

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    So the mac classics and the following similar models
    with 1.44MB drives weren't backwards compatible with the 800k disks?

  9. #9

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    Quote Originally Posted by DFinnigan View Post
    I wouldn't count on it. You did the floppy equivalent of partitioning a hard disk, and leaving some of the total capacity unused.
    I'm not counting on it. I was just adding to hjalfi's post that it does not take much to write a 800k image back to disk in a way a Mac with a SuperDrive can read.

  10. #10

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    Quote Originally Posted by maxtherabbit View Post
    So the mac classics and the following similar models
    with 1.44MB drives weren't backwards compatible with the 800k disks?
    The Mac Classic is. I've used and installed many software from original 800k disks on mine.

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