Fujitsu MJA2500BH Maintenance Manual - Page 275

6.4 Read-ahead Cache 6.4 Read-ahead Cache Read-ahead Cache is the function for automatically reading data blocks upon completion of the read command in order to read data from disk media and save data block on a data buffer. If a subsequent command requests reading of the read-ahead data, data on the data buffer can be transferred without accessing the disk media. As the result, faster data access becomes possible for the host. 6.4.1 Data buffer structure This device contains a data buffer. This buffer is divided into two areas: one area is used for MPU work, and the other is used as a read cache for another command. (See Figure 6.5) Example of 8 MB buffer For MPU work 8,192 KB (8,388,608 bytes) For R/W command Figure 6.5 Data buffer structure The read-ahead operation is done by the following commands. • READ SECTOR (S) (EXT) • READ MULTIPLE (EXT) • READ DMA (EXT) • READ FP DMA QUEUED C141-E293 6-13