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.