| Design firm | Intel |
|---|---|
| Introduced | Q1 2005[1] |
| Type | Dynamic frequency scaling |
Enhanced SpeedStep is a series ofdynamic frequency scaling technologies (codenamedGeyserville[2] and including SpeedStep,SpeedStep II, andSpeedStep III) built into someIntel'smicroprocessors that allow theclock speed of the processor to be dynamically changed (to differentP-states) by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizingpower draw and heat generation. EIST (SpeedStep III) was introduced in several Prescott 6 series in the first quarter of 2005, namely thePentium 4 660.[1] Intel Speed Shift Technology (SST) was introduced in IntelSkylake Processor.[3]
Enhanced Intel SpeedStep Technology is sometimes abbreviated asEIST. Intel's trademark of "Intel SpeedStep" was canceled due to the trademark being invalidated in 2012.[4]
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Running a processor at high clock speeds allows for better performance. However, when the same processor is run at a lower frequency (speed), it generates less heat and consumes less power. In many cases, thecore voltage can also be reduced, further reducing power consumption and heat generation. By using SpeedStep, users can select the balance of power conservation and performance that best suits them, or even change the clock speed dynamically as the processor burden changes.
The power consumed by a CPU with acapacitanceC, running at frequencyf and voltageV is approximately:[5]
For a given processor,C is a fixed value. However,V andf can vary considerably. For example, for a 1.6 GHzPentium M, the clock frequency can be stepped down in 200 MHz decrements over the range from 1.6 to 0.6 GHz. At the same time, the voltage requirement decreases from 1.484 to 0.956 V. The result is that the power consumption theoretically goes down by a factor of 6.4. In practice, the effect may be smaller because some CPU instructions use less energy per tick of the CPU clock than others. For example, when an operating system is not busy, it tends to issuex86 halt (HLT) instructions, which suspend operation of parts of the CPU for a time period, so it uses less energy per tick of the CPU clock than when executing productive instructions in its normal state. For a given rate of work, a CPU running at a higher clock rate will execute a greater proportion of HLT instructions. The simple equation which relates power, voltage and frequency above also does not take into account the static power consumption of the CPU. This tends not to change with frequency, but does change with temperature and voltage.
Microsoft has reported that there may be problems previewing video files when SpeedStep (or the AMD equivalentPowerNow!) is enabled under Windows 2000 or Windows XP.[6]
powercfg.exe command-line utility.[12]In contrast, AMD has supplied and supported drivers for its competingPowerNow! technology that work on Windows 2000, ME, 98, and NT.[15][16]