Hitachi T7K250 - Deskstar - Hard Drive Specifications page 231

Input parameters from the device on command complete
Sector Count
Sector Number, Cylinder High/Low, H
SRV
Bits 7 - 3 (Tag) contain the Tag of the completed command.
Bit 2 (REL) is cleared to zero.
Bit 1 (I/O) is set to one.
Bit 0 (C/D) is set to one.
Sector address of unrecoverable error (applicable only when an unrecoverable
error has occurred).
Cleared to 0.
Deskstar T7K250 Hard Disk Drive Specification
217