Hard Disk Geometry

Low-level format.

• to create data structures.

  • tracks - addresses start from outside.

  • cylinders - all tracks at a given address on all platters C ∈ [0, maxC ].

    • tracks can be addressed by the head number H ∈ [0, maxH ]

  • sectors - subdivision of tracks, typically 512 bytes S ∈ [1, maxS ]

Get one sector CHS.

• Cylinder address (C).

• Head number (H).

• Sector address (S).

Sectors

Distribution

Addressing schemes

Cylinder, Head, Sector (CHS) – used only on older systems.

• maximum addressable capacity 504 MB.

• way around the problem with fake geometry.

• but this translation was limited to address a maximum of 8,1 GB.

Logical Block Address (LBA).

• each sector has a unique address.

• the software doesn’t need to know the disk geometry.

• LBA/CHS conversion:

  • LBA = (C × maxH + H) × maxS + (S − 1)