Fujitsu MHT2040AT 用户手册
Operations
6-12
C141-E192-01EN
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.
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.
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 2 MB. 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 Figures 6.7 and 6.8.)
one area is used for MPU work, and the other is used as a read cache for another
command. (See Figures 6.7 and 6.8.)
For MPU work
For R/W command
For MPU work
2048 KB (2097152 bytes)
391 KB
(400384 bytes)
1657 KB
(1696768 bytes)
16 KB
(16384 bytes)
Figure 6.7 Data buffer structure (2 MB Buffer)
The read-ahead operation is done by the following commands.
•
READ SECTOR (s) (EXT)
•
READ MULTIPLE (EXT)
•
READ DMA (EXT)
•
READ DMA QUEUED (EXT)
•
READ STREAM PIO
•
READ STREAM DMA