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C141-E045-02EN 6 - 17
(3) Sequential read
When the disk drive receives the read command that targets the sequential address to the
previous read command, the disk drive starts the read-ahead operation.
a. Sequential command just after non-sequential command
When the previously executed read command is an non-sequential command and the last
sector address of the previous read command is sequential to the lead sector address of the
received read command, the disk drive assumes the received command is a sequential
command and performs the read-ahead operation after reading the requested data.
1) At receiving the sequential read command, the disk drive sets the DAP and HAP to
the sequential address of the last read command and reads the requested data.
Empty dataMis-hit data
2) The disk drive transfers the requested data that is already read to the host system with
reading the requested data.
Requested data
DAP
HAP
Mis-hit data Empty data
3) After completion of the reading and transferring the requested data to the host system,
the disk drive performs the read-ahead operation continuously.
Mis-hit data Requested data
DAP
HAP
Empty
data
Read-
ahead
data
DAP
HAP