SpeedStep

Lore & Background

Enhanced SpeedStep technology allows the clock speed of a processor to be dynamically changed by software, enabling a balance between power conservation and performance. Running a processor at a high clock speed allows for better performance, but running at a lower frequency generates less heat and consumes less power; in many cases, the core voltage can also be reduced, further reducing power consumption and heat generation. Users can select the balance that suits them, or even change the clock speed dynamically as processor burden changes.

The power consumed by a CPU with capacitance C, running at frequency f and voltage V is approximately proportional to C·V²·f. For a given processor, C is fixed, but V and f can vary considerably. For example, for a 1.6 GHz Pentium M, the clock frequency can be stepped down in 200 MHz decrements from 1.6 to 0.6 GHz, while the voltage requirement decreases from 1.484 to 0.956 V, theoretically reducing power consumption by a factor of 6.4. In practice, the effect may be smaller because some CPU instructions use less energy per tick than others; for instance, when an operating system is not busy, it tends to issue x86 HLT instructions, which suspend parts of the CPU, using less energy per tick than when executing productive instructions.

Microsoft has reported that there may be problems previewing video files when SpeedStep (or the AMD equivalent PowerNow!) is enabled under Windows 2000 or Windows XP. The Linux kernel has a subsystem called 'cpufreq' devoted to controlling operating frequency and voltage, and Solaris has supported SpeedStep since OpenSolaris SXDE 9/07.

Reader's Guide

Enhanced SpeedStep technology represents a significant development in processor power management, allowing dynamic adjustment of clock speed and voltage to balance performance with power consumption and heat generation. Its introduction in the Pentium 4 660 (Prescott 6 series) in early 2005 marked a step forward in making frequency scaling a standard feature for Intel processors. The technology's ability to reduce power consumption theoretically by a factor of 6.4 in some implementations, as seen with the Pentium M, highlights its potential impact on mobile computing and energy efficiency.

Operating system support has been a key factor in its adoption. Microsoft Windows XP built SpeedStep support into the Power Management console, allowing users to regulate processor speed indirectly through power schemes, though settings could only be modified via the powercfg.exe command-line utility. Older Windows versions required a special driver from the computer manufacturer, as Intel supplied no generic drivers. Linux's cpufreq subsystem and Solaris's support since OpenSolaris SXDE 9/07 broadened the technology's reach. The later introduction of Intel Speed Shift Technology with Skylake further evolved dynamic frequency control. The cancellation of Intel's SpeedStep trademark in 2012 did not affect the technology's continued use and development.

Did You Know?

• Enhanced SpeedStep is sometimes abbreviated as EIST.
• The technology was codenamed Geyserville and includes SpeedStep, SpeedStep II, and SpeedStep III.
• Intel's trademark for 'Intel SpeedStep' was canceled due to invalidation in 2012.
• Microsoft reported potential problems previewing video files when SpeedStep is enabled under Windows 2000 or Windows XP.