Other articles > X86 Glossary > Enhanced Intel Speedstep Technology (EIST)

Enhanced Intel SpeedStep Technology (EIST) is a power and thermal management technology developed by Intel. EIST was introduced as a means of enabling high performance while meeting the power-saving needs of a mobile computer system.

Essentially, EIST throttles the clock speed of a central processing unit (CPU) during periods requiring minimal demand. It then brings the clock speed back up to its maximum potential when demanded by the load . This allows a computer to save power when there is less to process, yet still achieve high performance when the demand is high.

The earlier, non-enhanced version of SpeedStep switched frequency and voltage between low and high levels in response to a current processor load. EIST builds on this by using the following strategies:

• Separating frequency and voltage changes, whereby voltage is stepped up or down in small increments separately from changes in frequency. Because of this, the processor is able to reduce system unavailability due to frequency change. This technique allows the system to switch between voltage and frequency states more often, improving power-performance balance.
• Clock partitioning and recovery, where the bus clock runs continuously even during state transitions. It continues running even when the core clock and the phase-lock loop are stopped. This allows for logic to remain active even when some of the CPU portions are currently stopped.

EIST reduces the latency inherent with changing the voltage-frequency pair (P-state), thus allowing those transitions to occur more frequently. This allows for more granular, demand-based switching and can optimize the power-to-performance balance, based on the demands of the applications.

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