Fujitsu MPD3XXXAH User Manual download pdf (Page 181)

C141-E072-01EN6 - 14

6.5.2 Caching operation

The caching operation is performed only at receipt of the following commands. The device

transfers data from the data buffer to the host system if the following data exist in the data buffer.

• All sector data to be processed by the command

• A part of data including the starting sector to be processed by the command

When a part of data to be processed exist in the data buffer, the remaining data are read from

the disk medium and are transferred to the host system.

(1) Commands that are object of caching operation

The following commands are object of caching operation.

• READ SECTOR (S)

• READ MULTIPLE

• READ DMA

When the caching operation is disabled by the SET FEATURES command, no caching

operation is performed.

(2) Data that are object of caching operation

The following data are object of caching operation.

1) Read-ahead data read from the disk medium in 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. When the sector data requested by the host does not finish storing in

the buffer for read cache, it is not object of caching operation. And also, when the

sequential hit occurs continuously, the caching data required by the host becomes invalid.

(3) Invalidating caching data

Caching data in the data buffer is invalidated in the following case.

1) Commands other than the following commands are issued (all caching data are invalidated)

• WRITE SECTOR(S)

• WRITE DMA

• WRITE MULTIPLE

2) Caching operation is disabled by the SET FEATURES command.

3) Command issued by the host is terminated with an error.

4) Soft reset or hard reset is executed, or power is turned off.

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