Commodore 1551 User Manual page 88

SEQUENTIAL FILE FORMAT
BYTE DEFINITION
ALL BUT FINAL SECTOR
0-1
Track and sector of next sequential data block.
2-255 254 bytes of data.
FINAL SECTOR
0,1
Null ($00), followed by number of valid data bytes in sector.
2-??? Last bytes of data. Any remaining bytes are garbage and may be ignored.
1551 RELATIVE FILE FORMAT
BYTE DEFINITION
DATA BLOCK
0,1
Track and sector of next data block.
2-255
254 bytes of data. Empty records contain $FF
(all binary ones) in the first byte followed by $00
(binary all zeros) to the end of the record. Partially
filled records are padded with nulls ($00).
SIDE SECTOR BLOCK
0-1
Track and sector of next side sector block.
2 Side sector number (0-5)
3 Record length
4-5
Track and sector of first side sector (number 0)
6-7 Track and sector of second side sector (number 1)
8-9
Track and sector of third side sector (number 2)
10-11
Track and sector of fourth side sector (number 3)
12-13
Track and sector of fifth side sector (number 4)
14-15
Traek and sector of sixth side sector (number 5)
16-255
Track and seetor pointers to 120 data blocks.
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