Operations
6-14 C141-E104-02EN
An unrecoverable write error occurs during write error retry, automatic alternate
assignment is performed.
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 2 MB 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).
for read commands for write commands for MPU work
2 MB (2,097,152 bytes)
1,048,576 bytes (2048 sector) 983,040 bytes (1920 sector) 65,536 bytes
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 issuance of the following commands. The
device transfers data from the data buffer to the host system at issuance 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.