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C141-E045-02EN 6 - 13
(3) Automatic alternate assignment
The device performs the automatic assignment at following case.
1) 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.
2) When a write error occurs and the error does not recovered.
6.5 Read-Ahead Cache
After read command which involves 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 256-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).
256 KB (262,144 bytes)
for write commandsfor MPU work
19,456 bytes
(38 sectors)
111,616 bytes (218 sectors)
131,072 bytes (256 sectors)
for read commands
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.