Disk Specification

Summary

• Physical Disk
  • Each 64DD disk contains 2 sides.
  • Each side a total of 1175 cylinder tracks over 8 different zones.
  • A track is also composed of 2 blocks.
  • A block is made of 90 sectors:
    • 85 user data sectors
    • 4 C2 error correction sectors
    • 1 gap sector (unused by the driver).
  • The sector size depends on the zone.
  • C1 error correction data for each sector is 7 bytes. This may or may not be outputted by the drive.
• Official Driver Process
  • The driver considers that each zone has a total of 10 or 12 defective tracks depending on development and retail disks.
    • This effectively means that 10 or 12 tracks of each zone are skipped.
  • For seek optimizations, the ordering of the blocks is interleaved between each track.
    • Track 0 : [LBA 0] [LBA 1]
    • Track 1 : [LBA 3] [LBA 2]
      Notice the swapped order in Track 1.
  • Side 0 Tracks are read from the start of the Zone, while Side 1 Tracks are read from the end of the Zone.
  • C1 error correction is processed by the drive, while C2 error correction is managed by the driver.

Physical Disk

Zones

Amount of Tracks, including defective tracks

Side 0 starts with Zone 0, Side 1 starts with Zone 1.

	Side 0	Side 1
Zone 0	158
Zone 1	158	158
Zone 2	149	158
Zone 3	149	149
Zone 4	149	149
Zone 5	149	149
Zone 6	149	149
Zone 7	114	149
Zone 8		114

Sector Size

This does not count the C1 size information, size is in bytes.
Add +8 for a full sector size with C1 info.

	Size
Zone 0	232
Zone 1	216
Zone 2	208
Zone 3	192
Zone 4	176
Zone 5	160
Zone 6	144
Zone 7	128
Zone 8	112

Driver Process

ROM & RAM Areas

The System Data of the disk contains information about the Disk Type, which basically changes the ratio of ROM (Read only) / RAM (rewritable) Areas. The Disk Type is given to the 64DD drive in a command which locks / unlocks the write protection for certain zones.

	ROM Area
Zone 0	Always
Zone 1	Always
Zone 2	Always
Zone 3	Type 1+
Zone 4	Type 2+
Zone 5	Type 3+
Zone 6	Type 4+
Zone 7	Type 5+
Zone 8	Type 6+