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12
Cheetah 18FC Product Manual, Rev. C
4.5.1
Caching write data
Write caching is a write operation by the drive that makes use of a drive buffer storage area where the data to
be written to the medium is stored while the drive performs the Write command.
Write caching is enabled independently of read caching. Write caching is enabled by default. To disable the
write cache, use the Write Caching Enable (WCE) bit.
For write caching, the same buffer space and segmentation is used as set up for read functions. When a write
command is issued, the cache is first checked to see if any logical blocks that are to be written are already
stored in the cache from a previous read or write command. If there are, the respective cache segments are
cleared. The new data is cached for subsequent read commands.
If a 10-byte CDB Write command (2Ah) is issued with the data page out (DPO) bit set to 1, no write data is
cached, but the cache segments are still checked and cleared, if need be, for any logical blocks that are being
written.
If the number of write data logical blocks exceeds the size of the segment being written into when the end of
the segment is reached, the data is written into the beginning of the same cache segment, overwriting the data
that was written there at the beginning of the operation. However, the drive does not overwrite data that has not
yet been written to the medium.
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