Fujitsu MCE3130AP, MCF3064AP, MCE3064AP manual Cache function, Data buffer, Read cache

4.4.5Cache 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.

4.4.5.1Data 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.

4.4.5.2Read 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 prereads the specified sector, then prereading the next sector when receiving a READ (10) or READ (12) command (called Read command in this document). While prereading the next sector, the ODD transfers the data in the sector specified by the command.

When data in the sector specified by the host hits preread data, the ODD transfers data directly from the buffer without any mechanical operation.

Preread stops under the following conditions:

!Access to the alternate sector

!Read error and retry

!Logical zone boundary of media

!When a read command is received for a sector not continuous from the sector specified by the previous read command

!When a command other than Read is received

!When the data buffer is full

!Media ejection instruction using the Eject switch

!Hardware reset, software reset, DEVICE RESET command is received, or power-off

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