Three tracks of this disk can't be read with a standard DOS due to an alterated address epilog. The usual $DE $AA was changed to $DE $XX where $XX is different for each track. We need to tell DOS to ignore epilogue to get a copy of the original disk: POKE 47516,234 ($B99C:$EA) POKE 47517,234 ($B99D:$EA) RUN COPYA Here the trick is that the modified bytes are used as keys to decode the following data read from the disk. Use a disk editor and look at: track $00 sector $0C byte $00 and change $A0 $00 $98 - LDX #$00, TYA to $20 $E0 $42 - JSR $42E0, then write this little routine starting at byte $E0: A9 AF - LDA #$AF 85 00 - STA $00 A9 BE - LDA #$BE 85 01 - STA $01 A9 CD - LDA #$CD 85 02 - STA $02 85 03 - STA $03 A0 00 - LDY #$00 \ this is the code we previously changed to JSR $42E0 98 - TYA / 60 - RTS This put in the zero page the original modified ("original modified" is an oximoron?) epilogue byte so the program can go on with the decoding step.