IBM DTCA-23240 - Travelstar 3.2 GB Hard Drive, Specifications

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Each time this algorithm decides that the current burst of commands is not yet complete, it places the device
in Performance Idle mode. This means another command will arrive very soon, and the response to it can
now be instantaneous without the delay associated with conventional idle. Since bursts usually contain tens
of commands, performance is improved.
When this algorithm decides the current burst of commands is complete, it knows with high probability that
the next command will not occur for a relatively long time (seconds). To conserve power, this feature places
the device in Active Idle mode, then performs a seek to the mid-band and enters a low power state.
The optimal time to enter Active Idle is variable depending on the users recent behavior. It is not possible
to achieve the same level of savings with a fixed entry time into Active Idle because every users data and
access pattern is different. The optimum entry time changes over time.
To recover to Active mode from Active Idle requires about 40 ms. This does not represent a significant
performance impact because it is a relatively rare event, and because a new burst of commands almost
always begins with a seek to a new location which requires the time anyway. Throughput is maintained
because Active Idle is entered only when a long idle interval is anticipated.
The same algorithm works for entering into Low Power Idle mode, which consumes less power and need
more recovery time switching from this mode to Active mode.
General Operation Descriptions
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