4.4 Various Processes
After automatic alternate assignment terminates successfully, the ODD does not report any error.
4.4.5 Cache function
The ODD supports the read cache and MO write cache.
The read cache consists of the read ahead cache and the LRU cache that reads write data remaining in the data buffer.
The read ahead cache allows for data transfer at a near effective transfer speed during continuous read operation without causing any delay owing to rotation latency. LRU allows for data transfer with no mechanical operation if write and read operations are executed frequently on the same sector.
The MO write cache writes data in batch mode during continuous write operation, thus reducing positioning operations depending on the buffer size and recovering the write throughput.
4.4.5.1 Data buffer
The ODD uses part of the buffer area as work memory for control firmware and the remaining area as a buffer. The data buffer consists of plural segments and contains write data of plural segments.
4.4.5.2 Read cache
The ODD enables the read ahead cache and LRU cache when the cache function is enabled. When the read cache is enabled, the ODD contiguously
When data in the sector specified by the host hits
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Read error
When the data buffer is full
Media ejection instruction using the Eject switch
When It is decided that the performance becomes better by stopping pre- reading and give priority to other processings.
When the cache is enabled, the buffer contains data transferred from the host with a write command. If a read command is issued to the sector address at this time, the ODD directly transfers data to the
