This article is a cursory discussion of Intel SpeedStep Technology (SpeedStep) and Enhanced Intel SpeedStep Technology (EIST). The goal is more to illuminate what these technologies are and are not. The detail of how each technology works is not addressed here. Intel SpeedStep exists in several versions, dating back to the Pentium III processor. Intel's most current implementation, EIST (Enhanced Intel SpeedStep Technology), includes realtime Level 2 cache capacity variation.
It is worthy to note that AMD provides a similar group of technologies known as PowerNow!, Cool'n'Quiet, and Optimized Power Management (an adaptation of PowerNow! for newer Opterons).
Regardless of the processor type or class, and without regard to any particular generation, each of these technologies perform the same basic task - temporarily alter the operating frequency and power consumption of the processor(s) according to demand. Oversimplified, this is accomplished by altering the base frequency of the CPU, core voltage, or a combination of both. Low demand means less power needed, and obviously, high demand means more power.
Wiki arguably has the most concise definition (see link below) :
SpeedStep is a trademark for a series of dynamic frequency scaling technologies built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat dissipation.
Because the scope of this article is narrowly focused, all the variants of this class of technology will be referenced as SpeedStep. Sorry, AMD. No disrespect intended.
SpeedStep is not really a single thing. SpeedStep is a group of components working together. In a manner of speaking, SpeedStep is a system. Remove any individual component and SpeedStep will no longer function.
SpeedStep requires -
Processor with SpeedStep technology
A chipset, BIOS, and voltage regulator that support it
Operating System support
A driver (for older variants or operating systems without native kernel support)
SpeedStep is not related to overclocking. It has nothing to do with the default or manually adjusted frequency that a CPU will operate at. Several computer BIOS settings are available to modify or control the variables that determine a CPU's operating frequency and/or core voltage. SpeedStep can be used in conjunction with these settings. You can have an overclocked computer that will clock down when all that extra power is not in use.
Overclocking (and under underclocking) works during POST (power on self test) and is persistent during boot and when the operating system loads. If you have an overclocked system, you can see the overclocked frequency onscreen during POST. If you have an underclocked system, you can see the underclocked frequency onscreen during POST.
SpeedStep does not function during POST, nor does it function during the boot process. Remember, SpeedStep requires an operating system to function, and the operating system has not loaded at that point. The frequency value presented onscreen during POST is a result of BIOS settings and not the SpeedStep system. If you have a properly configured and properly powered motherboard, the CPU frequency you see during POST is the standard operating frequency for your CPU. If the POST screen shows a CPU frequency lower than the rated speed of your processor, something is amiss in your BIOS settings or with the power system (PSU, battery and/or battery CMOS battery).
Once the operating system has loaded, you have several options in how SpeedStep can fulfill your needs. In Windows, these settings can be found in the Power Control Panel or under Power Options. See your User Guide or favorite web source for more information.
A nice forum thread presenting a concise and easy to read explanation on how SpeedStep works and how to manage it. Written by Chilly at HardwareCanucks http://www.hardwarecanucks.com/forum/cpus-motherboards/14026-whats-up-my-cpu-speedstep-f-q.html
I am not a member at that site nor am I affiliated with it in any way.
at WikiPedia - http://en.wikipedia.org/wiki/SpeedStep
at Intel - (SpeedStep links not found) See EIST http://www.intel.com/technology/product/demos/eist/demo.htm
at Wikipedia - http://en.wikipedia.org/wiki/PowerNow!
at AMD - http://www.amd.com/us/products/technologies/amd-powernow-technology/Pages/amd-powernow-technology.aspx
at Wikipedia - http://en.wikipedia.org/wiki/Cool%27n%27Quiet
at AMD - http://www.amd.com/us/products/technologies/cool-n-quiet/Pages/cool-n-quiet.aspx
Links for AMD's Optimized Power Management are not provided. Users of that technology are not this article's target audience.
This article makes use of registered trade / service marks. Each belongs to its respective owner and is referenced herein for instructional purposes only.