# How to turn raw 1440KB HFS floppies into DMG files
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# Create floppy image, 80 sectors bigger than 2880 so
# it can contain partition table information that the
# original floppy never did
hdiutil create -fs HFS -sectors 2960 floppy
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# attach it to turn it into usable but don't mount
hdid -nomount floppy.dmg
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# spew raw data into device.  could be disk[0-9]+
dd if=file.raw of=/dev/disk1s2
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# eject the virtual disk.
hdiutil eject /dev/disk1
# floppy.dmg now contains a valid partition table
# plus the raw HFS filesystem, so OSX will know how
# to use it!