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C141-E034-02EN 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 128-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).
16,896 bytes48,640 bytes (95 sectors)65,536 bytes (128 sectors)
128 KB (131,072 bytes)
for read commands for write commands for MPU work
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.