880kB 3.5” DSDD

Amiga disks use MFM, but don’t use IBM scheme. Instead, the entire track is read and written as a unit, with each sector butting up against the previous one. This saves a lot of space which allows the Amiga to not just store 880kB on a DD disk, but also allows an extra 16 bytes of metadata per sector.

This metadata is mostly unused, so the default for FluxEngine is to ignore it and just use the 512 bytes of main sector data. If you want it, specify a 528-byte sector size. The metadata will come after the user data.

Bizarrely, the data in each sector is stored with all the odd bits first, and then all the even bits. This is tied into the checksum algorithm, which is distinctly subpar and not particularly good at detecting errors.

Options

  • Sector size:
    • without_metadata: 512-byte sectors
    • with_metadata: 528-byte sectors

Examples

To read:

  • fluxengine read amiga -s drive:0 -o amiga.adf

To write:

  • fluxengine write amiga -d drive:0 -i amiga.adf

References

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