Reconstructing the GEOS 2.0 master images from a pile of broken diskettes #VintageComputing #Software #Floppies @pagetable

Michael Steil writes on pagetable.com about reconstructing the diskette set for GEOS 2.0 (the German edition) from a pile of broken GEOS disks that were sent in for replacement. First – what was GEOS?

GEOS (Graphic Environment Operating System) is a discontinued operating system from Berkeley Softworks (later GeoWorks). Originally designed for the Commodore 64 released in 1986. Wikipedia

Michael looks to reconstruct the original diskette contents based on a pile of defective disks.

The original disk set consisted of four double-sided disks. Of my 50 disks, this is the distribution:

  • 21x Disk 1/4: System
  • 18x Disk 2/4: Backup
  • 7x Disk 3/4: GeoSpell
  • 4x Disk 4/4: Drivers

GEOS disks 1 and 2 are specially mastered for copy protection purposes: When looking at the raw bits on disk, the gaps between sector headers and the sector data contain a signature that cannot be reproduced by an unmodified 1541 drive, and that will be destroyed whenever writing a sector.

With analysis in the post, the conclusion:

It was possible to recreate the original masters. The GEOS serial number system made things more complicated than it should have been, but the copy protection signature then made things a lot easier again!

You can see the detailed post here with copies of the restored data diskettes.

Note: the reverse engineered source for GEOS is available on GitHub.


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