Difference between revisions of "GEOS Protection"

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On track 21 in the header trail and sector trail the trail has to end with 55 67 55 55 67 before the following sync.
 
On track 21 in the header trail and sector trail the trail has to end with 55 67 55 55 67 before the following sync.
 
Header trails are checked for sector 0 - 18, sector trails for sector 0 to 17 (track trail after last sector is not checked).
 
Header trails are checked for sector 0 - 18, sector trails for sector 0 to 17 (track trail after last sector is not checked).
 +
 +
Example from GEOS 2.5:
 +
 +
  sync 33
 +
  ; header
 +
  gcr 08
 +
  begin-checksum
 +
      checksum 13
 +
      ; sector
 +
      gcr 00
 +
      ; track
 +
      gcr 15
 +
      ; id2
 +
      gcr 4a
 +
      ; id1
 +
      gcr 4c
 +
  end-checksum
 +
  gcr 0f
 +
  gcr 0f
 +
  ; Trk 21 Sec 0
 +
  bytes 55 55 '''55 67 55 55 55 67'''
 +
  bits 111111
 +
 +
  sync 34
 +
  ; data
 +
  gcr 07
 +
  begin-checksum
 +
      gcr 15 08 ...
 +
      checksum 76
 +
  end-checksum
 +
  gcr 00
 +
  gcr 00
 +
  bytes 55 55 '''55 67 55 55 55 67'''
 +
  bits 111111
 +
 +
  sync 34
 +
  ; header
 +
  
 
There is an extensive description at [https://www.c64-wiki.de/wiki/GEOS-Kopierschutz GEOS protection (german)]
 
There is an extensive description at [https://www.c64-wiki.de/wiki/GEOS-Kopierschutz GEOS protection (german)]

Revision as of 21:01, 11 January 2021

On track 21 in the header trail and sector trail the trail has to end with 55 67 55 55 67 before the following sync. Header trails are checked for sector 0 - 18, sector trails for sector 0 to 17 (track trail after last sector is not checked).

Example from GEOS 2.5: 

  sync 33
  ; header
  gcr 08
  begin-checksum
     checksum 13
     ; sector
     gcr 00
     ; track
     gcr 15
     ; id2
     gcr 4a
     ; id1
     gcr 4c
  end-checksum
  gcr 0f
  gcr 0f
  ; Trk 21 Sec 0
  bytes 55 55 55 67 55 55 55 67
  bits 111111

  sync 34
  ; data
  gcr 07
  begin-checksum
     gcr 15 08 ...
     checksum 76
  end-checksum
  gcr 00
  gcr 00
  bytes 55 55 55 67 55 55 55 67
  bits 111111

  sync 34
  ; header


There is an extensive description at GEOS protection (german)

Pages that refer to this protection

Retrieved from "https://preservation64.de/index.php?title=GEOS_Protection&oldid=24228"