visualize_1541 is a tool that creates visualizations of the data layout on G64 Commodore 1541 disk images.


This representation is useful to visualize custom disk formats and differences in gap sizes.

  • Every track starts at the bottom and is drawn counter-clockwise.

  • Green represents the data. Darker areas have more 0-bits.

  • Red represents a longer sequence of 1-bits.

  • Blue represents a longer sequence of 0-bits.

    python disk.g64 disk.png


This representation is useful to visualize errors on Commodore-formatted disks. The tool decodes SYNC marks and sector headers.


  • Every pack of 17-21 lines is a track, numbered 1-41.

  • Every line within a pack is one sector.

  • The raw sector contents are drawn from left to right.

  • The cyan part is the header, the green part the data.

  • Black is 0, cyan/green is 1.

  • White represents missing header or sector sections.

    python disk.g64 disk.png

More Information

There are two articles about these tools:


These are some limitations of the tool for the circular representation:

  • Because the Pillow library cannot draw antialiased lines, the tool renders the image at 16x (!) the resolution and scales it down at the end. This uses a lot of memory, yet there are still Moiré artifacts. Using a different image library would be a good idea.
  • Red areas (SYNCs marks) show up as soon as there are 8 1-bits. SYNC detection on the 1541 requires at least 10. (The sector-by-sector tool contains logic for correct SYNC detection that should be ported over.)
  • The data area shows the GCR data. An option should be added to show the GCR-decoded data.
  • nibtool .nbz files are better suited as sources, the tool should be extended to support them.