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230229 230229764321 Figure 6.8 Alternate cylinder assignment 2 alternate cylinders are provided for each head in zone 12 (inner side). When an access request to physical sector 5 is specified, the device accesses the alternated sector in the alternate cylinder instead of sector 5. When an access request to sectors next to sector 5 is specified, the device seeks to cylinder 0, head 0, and continues the processing. (3) Automatic alternate assignment The device performs the automatic alternate assignment when ECC correction performance is increased during read error retry, a read error is recovered. Before automatic alternate assignment, the device performs rewriting the corrected data to the erred sector and rereading. If no error occurs at rereading, the automatic alternate assignment is not performed. An unrecoverable write error occurs during write error retry, automatic alternate assignment is performed. C141-E050-02EN 6-13 Operations 6.5 Read-Ahead Cache After read command which involes read data from the disk medium is completed, the read-ahead cache function reads the subsequent data blocks automatically and stores the data to the data buffer. When the next command requests to read the read-ahead data, the data can be transferred from the data buffer without accessing the disk medium. The host can thus access data at higher speed. 6.5.1 Data buffer configuration The drive has a 512-KB data buffer. The buffer is used by divided into three parts; for read commands, for write commands, and for MPU work (see Figure 6.9). 512 MB (524,288 bytes) for read commands for write commands for MPU work 262,144 byte (512 sector) 131,072 byte (256 sector) 131,072 byte Figure 6.9 Data buffer configuration The read-ahead operation is performed at execution of the READ SECTOR(S), READ MULTIPLE, or READ DMA command, and read-ahead data is stored in the buffer for read commands. 6.5.2 Caching operation Caching operation is performed only at issurance of the following commands. The device transfers data from the data buffer to the host system at issurance 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. 6-14 C141-E050-02EN 6.5 Read-Ahead Cache • 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 issurance of read command is performed to the data buffer for read command prioritily, 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. (3) Invalidating caching data Caching data in the data buffer is invalidated in the following case. 1) Following command is issued to the same data block as caching data. - WRITE SECTOR(S) - WRITE DMA - WRITE MULTIPLE 2) Command other than following commands is issued (all caching data are invalidated) - READ SECTOR (S) - READ DMA C141-E050-02EN 6-15 Operations - READ MULTIPLE - WRITE SECTOR(S) - WRITE MULTIPLE -WRITE VERIFY SECTOR(S) 3) Caching operation is inhibited by the SET FEATURES command. 4) Issued command is terminated with an error. 5) Soft reset or hard reset occurs, or power is turned off. 6) The device enters the sleep mode. 7) Under the state that the write data is kept in the data buffer for write command as a caching data, new write command is issued. (write data kept until now are invalidated) 6.5.3 Usage of read segment This subsection explains the usage of the read segment buffer at following cas...

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