HP C2233 Product Description Manual page 50

Buffer Management
3-10 Product Features
entries will be removed from the spares allocation table
and replaced by a single track spare entry.
This product incorporates a 64-Kilobyte buffer to provide
performance enhancements. Upon receiving a READ
command, the controller will load the requested data plus
the balance of the track into the first half of the buffer. If
the next READ command asks for data not already resident
in the buffer, the new data and the balance of the track is
loaded into the second half of the buffer. The balance of
both tracks tracks (up to 64-Kilobytes) are now loaded into
the buffer. The data from either of these tracks can be
read independently by future READ commands without
accessing the media.
If a later READ command requests data not in either half
of the buffer, the new data is accessed from the media and
loaded into the half of the buffer that was not accessed
last. The track that was accessed last is saved in the buffer.
In this manner, the two tracks most recently accessed
are retained in the buffer for higher performance READ
operations. The controller manages the buffer contents
with a Look Ahead Read function. The amount of data
loaded into the buffer is determined by the Look Ahead
Read function.
Look Ahead Reads
The Look Ahead Read capability can improve the
performance of a drive doing sequential READs by
preloading
the
track buffer with the data most likely
to
be
requested with the next READ command. After a READ
command is received by the controller, the drive seeks
to
the proper track and loads the requested data into the
buffer. While that data is being transferred to the host, the
Look Ahead Read function continues to read the remainder
of the current track into the buffer. If in subsequent READ
requests, the host asks for the following blocks on the same
track, they will already be in the buffer, and the data
DRAFT
10/24/90 11:07