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C141-E045-02EN6 - 14
6.5.2 Caching operation
Caching operation is performed only at issuance of the following commands. The device
transfers data from the data buffer to the host system at issuance of following command if
following data exist in the data buffer.
• All sectors to be processed by the command
• A part of data including load sector to be processed by the command
When a part of data to be processed exist in the data buffer, remaining data are read from the
medium and are transferred to the host system.
(1) Commands that are object of caching operation
Follow commands are object of caching operation.
• READ SECTOR (S)
• READ MULTIPLE
• READ DMA
When caching operation is disabled by the SET FEATURES command, no caching operation
is performed.
(2) Data that are object of caching operation
Follow data are object of caching operation.
1) Read-ahead data read from the medium to the data buffer after completion of the command
that are object of caching operation.
2) Data transferred to the host system once by requesting with the command that are object of
caching operation (except for the cache invalid data by some reasons).
3) Remaining data in the data buffer (for write command) transferred from the host system by
the command that writes data onto the disk medium, such as the WRITE SECTOR (S),
WRITE DMA, WRITE MULTIPLE.
Followings are definition of in case that the write data is treated as a cache data. However,
since the hit check at issuance of read command is performed to the data buffer for read
command priority, caching write data is limited to the case that the hit check is missed at the
data buffer for read command.
• When all data requested by the read command are stored in the data buffer for write
command (hit all), the device transfers data from the data buffer for write command. At
this time, the read-ahead operation to the data subsequent to the requested data is not
performed.
• Even if a part of data requested by the read command are stored in the data buffer for
write command (hit partially), all data are read from the disk medium without transferring
from the data buffer for write command.