Specifications

DRQ is the data request bit. It is set to 1 when the drive is ready to
transfer a word or byte of data between the host and the data
port. The drive is busy whenever DRQ or BSY bits are set to 1.
When the DRQ bit is set to 1, the host may read or write any of
the registers including the Command register.
CORR is the corrected data bit. It is set to 1 when a correctable data
error has been encountered and the data has been corrected.
This condition does not end a multisector read operation. This
bit is set to 0 when a new command is serviced.
IDX is the index bit. This bit usually contains a 0, except once per
disc revolution when it is toggled from 0 to 1 and back to 0.
ERR is the error bit. It is set to 1 when the previous command ended
in some type of error. The other bits in the Status register, and
the bits in the Error register, have more information as to the
cause of the error. This bit is set to 0 when a new command is
serviced.
22 ATA Interface Reference Manual, Rev. C