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A local shop wanted my help - a customer had old documents on a Mac floppy. It had been years and years since I had my sights on a Mac with a floppy drive. I f

A local shop wanted my help - a customer had old documents on a Mac floppy. It had been years and years since I had my sights on a Mac with a floppy drive. I figured I could help anyway. First, I checked that the floppies weren't in DOS/Windows format. A long shot, but for a short while it was not unheard of to use DOS floppies as the lingua franca between Macs and PCs. Nah, that wasn't it. It was a real Mac floppy. No PC could read it. A Greaseweazle to the rescue! Created a floppy image. But how to read it? Turns out there's a Mac emulator on the web you can just drop a floppy image into, complete with MS Word 5 for Mac to read the document, export it to RTF and Bob's your uncle!

duskwuff 3y ago
> Turns out there's a Mac emulator on the web you can just drop a floppy image into... For the record: I think you're talking about https://infinitemac.org/ https://infinitemac.org/ - right?
- actionfromafar 3y ago
  I think so, but at a glance I can't find where I can upload files to infinitemac...
  - duskwuff 3y ago
    Drag and drop the file into the browser window. (Or hover over the Apple icon in the lower left and click "Load File".) If it's a disk image, it'll mount that; otherwise, it'll be copied to the VM as a file.
77pt77 3y ago
> Created a floppy image. How? Most PC floppy controllers were not "low level" enough to read those disks. You even mention that in your comment.
- csande17 3y ago
  The Greaseweazle device discussed in the article appears to be a specially-designed floppy controller that is low-level enough to read arbitrarily formatted disks.
  - YZF 3y ago
    IIRC Macs disks had different density for different sectors. The sectors on the outside had more data than sectors on the inside. I'm surprised a PC disk drive can read those, I'd have expected that to be impossible. I certainly have never heard of anyone doing that while PCs and Macs with floppy disks were around. EDIT: ok. it seems like this specific device is flexible enough. cool.
    - actionfromafar 3y ago
      Back in the day, Amiga could read Amiga floppies (of course), PC floppies and Mac floppies, using standard floppy drives.
      - 77pt77 3y ago
        Read and write. Again, I think it was just the controller delegated some signal processing to the rest of the hardware.
- deleted 3y ago
  [deleted]
somat 3y ago
This made me curious, why were pc floppy drive controllers unable to read mac formatted disks. my first thought was the variable sectors per cylinder, I mean sure the OS is not going to like it but what about the the actual capability of the controller. So I found a data sheet for a fairly modern fd controller(the NCT6776F all in one) Now I am not super sure, however if I am reading the data sheet correctly it looks like you could, if you were insane enough to spend the time on a lowlevel custom driver, format each track with a different number of sectors. my next thought was the variable speed, this might be it, the pc floppy controller has no command to change drive speed, but I was not convinced, it may not be as efficient, but I could think of no reason it could not read still read the tracks at a fixed speed. But I think the real reason a pc controller could not read apple floppies was that the on disk magnetic layout was GCR and the pc controller only understands MFM and FM, which ties into and changed my mind about the drive speed. if not designed for it the controller would not be happy about different sized magnetic zones. https://media.digikey.com/pdf/Data%20Sheets/Nuvoton%20PDFs/NCT6776F,D.pdf https://media.digikey.com/pdf/Data%20Sheets/Nuvoton%20PDFs/N... https://en.wikipedia.org/wiki/List_of_floppy_disk_formats https://en.wikipedia.org/wiki/List_of_floppy_disk_formats As a fun tangent I learned there are commands in the controller for a tape drive . I have never seen(or even heard of) a tape drive on a floppy port, how common was it to have one?
- rasz 3y ago
  For variable number of sectors per cylinder you either need control over bitrate or motor speed.
  - somat 3y ago
    Not an expert, I just read the datasheet but the format command takes The number of data bytes written in a sector Sectors per Cylinder Gap Length Data Pattern Then while the command is executing it takes(or might give... I am not real clear on this part) Cylinder Number Head Number Record The number of data bytes written in a sector So the hacker in me says why cant you say you want to format the disk then only format one cylinder. then do it again with another cylinder but this time with a different number of sectors. Reading and writing such a franken disk is left as an exercise for the reader. Honestly the whole exercise might be a fun weekend messing with assembly trying to see what contortions you could get the disk controller to do. It also sounds like a huge pain, I think I would want some sort of low level "stub" os, that does nothing bet gets the system initialized in a known state. then you could proceed to engage in severe sadomasochism, locking up your system in strange and mysterious ways.

duskwuff 3y ago

> Turns out there's a Mac emulator on the web you can just drop a floppy image into... For the record: I think you're talking about https://infinitemac.org/ https://infinitemac.org/ - right?

actionfromafar 3y ago
I think so, but at a glance I can't find where I can upload files to infinitemac...
- duskwuff 3y ago
  Drag and drop the file into the browser window. (Or hover over the Apple icon in the lower left and click "Load File".) If it's a disk image, it'll mount that; otherwise, it'll be copied to the VM as a file.

77pt77 3y ago

> Created a floppy image. How? Most PC floppy controllers were not "low level" enough to read those disks. You even mention that in your comment.

csande17 3y ago
The Greaseweazle device discussed in the article appears to be a specially-designed floppy controller that is low-level enough to read arbitrarily formatted disks.
- YZF 3y ago
  IIRC Macs disks had different density for different sectors. The sectors on the outside had more data than sectors on the inside. I'm surprised a PC disk drive can read those, I'd have expected that to be impossible. I certainly have never heard of anyone doing that while PCs and Macs with floppy disks were around. EDIT: ok. it seems like this specific device is flexible enough. cool.
  - actionfromafar 3y ago
    Back in the day, Amiga could read Amiga floppies (of course), PC floppies and Mac floppies, using standard floppy drives.
    - 77pt77 3y ago
      Read and write. Again, I think it was just the controller delegated some signal processing to the rest of the hardware.
deleted 3y ago
[deleted]

somat 3y ago

This made me curious, why were pc floppy drive controllers unable to read mac formatted disks. my first thought was the variable sectors per cylinder, I mean sure the OS is not going to like it but what about the the actual capability of the controller. So I found a data sheet for a fairly modern fd controller(the NCT6776F all in one) Now I am not super sure, however if I am reading the data sheet correctly it looks like you could, if you were insane enough to spend the time on a lowlevel custom driver, format each track with a different number of sectors. my next thought was the variable speed, this might be it, the pc floppy controller has no command to change drive speed, but I was not convinced, it may not be as efficient, but I could think of no reason it could not read still read the tracks at a fixed speed. But I think the real reason a pc controller could not read apple floppies was that the on disk magnetic layout was GCR and the pc controller only understands MFM and FM, which ties into and changed my mind about the drive speed. if not designed for it the controller would not be happy about different sized magnetic zones. https://media.digikey.com/pdf/Data%20Sheets/Nuvoton%20PDFs/NCT6776F,D.pdf https://media.digikey.com/pdf/Data%20Sheets/Nuvoton%20PDFs/N... https://en.wikipedia.org/wiki/List_of_floppy_disk_formats https://en.wikipedia.org/wiki/List_of_floppy_disk_formats As a fun tangent I learned there are commands in the controller for a tape drive . I have never seen(or even heard of) a tape drive on a floppy port, how common was it to have one?

rasz 3y ago
For variable number of sectors per cylinder you either need control over bitrate or motor speed.
- somat 3y ago
  Not an expert, I just read the datasheet but the format command takes The number of data bytes written in a sector Sectors per Cylinder Gap Length Data Pattern Then while the command is executing it takes(or might give... I am not real clear on this part) Cylinder Number Head Number Record The number of data bytes written in a sector So the hacker in me says why cant you say you want to format the disk then only format one cylinder. then do it again with another cylinder but this time with a different number of sectors. Reading and writing such a franken disk is left as an exercise for the reader. Honestly the whole exercise might be a fun weekend messing with assembly trying to see what contortions you could get the disk controller to do. It also sounds like a huge pain, I think I would want some sort of low level "stub" os, that does nothing bet gets the system initialized in a known state. then you could proceed to engage in severe sadomasochism, locking up your system in strange and mysterious ways.