## Storage Device Driver Reference

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### BPB and Get Device Parameters for Extended Volumes

For purposes of the BIOS Parameter Block (BPB) and Get Device Parameters ( generic IOCtl), an extended volume appears to the system as a fixed disk. The extended boot record corresponds to the Master Boot Record of a real fixed disk and the logical block device corresponds to the primary DOS partition.

This means the BPB of the logical DOS block device of the extended volume describes the environment in the extended volume. This consists of the extended boot record and the logical block device. The meaning of the fields is consistent with the meaning of the fields for the primary DOS partition; they relate to the entire physical disk, the primary DOS partition, and the Master Boot Record. For example, the number of hidden sectors is the distance from the beginning of the extended boot record (of the extended volume in question) to the start of the logical DOS block device (the DOS Boot Record). The number of sectors field describes only the logical block device, just as it normally only describes the primary DOS partition.