GEOS Protection

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

• GEOS DeskPack ‎ (← links)
• Descriptions of old disk copy protections ‎ (← links)
• GEOS GeoPublish ‎ (← links)
• GEOS 64 2.5 ‎ (← links)
• GEOS GeoCalc C128 ‎ (← links)
• GEOS GeoCalc C64 ‎ (← links)
• GEOS GeoFile ‎ (← links)
• GEOS GeoFile C128 ‎ (← links)
• GEOS 64 2.01 ‎ (← links)
• GEOS 128 2.01 ‎ (← links)
• GEOS 64 2.0 ‎ (← links)
• GEOS GeoWrite Workshop ‎ (← links)
• GEOS GeoWrite Workshop 128 ‎ (← links)
• GEOS 1.3 ‎ (← links)