10. Extended CHS, ECHS Mode

• ECHS is used for drives between 504 MB and 8 GB

  • CHS addressing is limited to

    • 10 bits for cylinder (<=1024)

    • 8 bits for head (<=256), and

    • 6 bits for sector (<=63 since first sector is 1.)

• In ECHS, the actual C value is divided by 2 and the H value multiplied by 2 until:

  • C < 1024 or H >= 255