Processor Performance Technology

Overall, power consumption is one of the biggest issues faced when designing mobile processors and systems. Most laptops are designed to run off battery power when disconnected from an AC power source. The less power required, the longer the system can run between recharges. In this case, battery life is not so much how many times you can discharge and recharge (expressed as the total number of cycles), but how long each cycle lasts. The less power the system requires, the greater the time you can run off an existing charge. Conserving power when connected to AC can also be useful for reducing component temperatures and heat generation in a laptop.

The Mobile Pentium III/Celeron, Pentium 4, Pentium M, AMD K6-2P, AMD K6-IIIP, AMD K6-III+, AMD Mobile Athlon 4, AMD Mobile Duron, AMD Mobile Athlon 64, AMD Mobile Sempron, and AMD Turion 64, as well as the Transmeta processors all feature processor performance-control technology to allow for longer battery life in mobile operation, as well as reduced thermal generation when under AC power. Intel calls this technology SpeedStep (originally code-named Geyserville), AMD calls it PowerNow!, and Transmeta calls it LongRun. This technology enables these processors to optionally reduce both speed and voltage when running on batteries. Earlier processors could reduce speed using SL technology, but by also reducing voltage, the overall power consumption (and heat production) is significantly reduced as well. More recent versions of this technology allow modes to be dynamically switched based on processor demand, not just by whether the system is running on battery or AC power.

Although processor performance-control technology is mainly designed to work when the laptop is running on battery power, it can also be used dynamically when under AC power to help reduce CPU temperature and energy consumption. When the laptop computer is connected to the AC outlet, CPU speed and voltage are normally at or near their maximum. When powered by a battery, the processor automatically drops to a lower frequency (by changing ratios, the bus frequency remains constant) and voltage, thus conserving battery life while still maintaining a relatively high level of performance. In most cases, the actual power consumption drops by half, which means about double the battery life as compared to full power, while reducing speed by only a small amount. For example, a 3.06GHz Mobile Pentium 4 consumes up to 101.4W at full power (3.06GHz and 1.55V), whereas in SpeedStep mode, the power consumption drops to only 40.9W (1.6GHz and 1.2V). This means that although power consumption drops by nearly 60%, the speed drops by only about 48%.

When the system is first powered up, the processor starts in the lower of its two speeds; that is, it starts in Battery Optimized mode. From there, BIOS, driver, or operating system instructions can rapidly switch the processor from mode to mode.

The requirements for this technology to work are as follows:

• A processor that supports SpeedStep/PowerNow!/LongRun technology
• A supporting motherboard (chipset, BIOS, and voltage regulator)
• A supporting operating system (Windows 9x/Me, Windows NT/2000/XP)
• SpeedStep/PowerNow!/LongRun driver (included with XP)

In general, all laptops that came with processors supporting performance-control technology included all of the other required support as well. Note that although it is possible to upgrade processors in many laptops, you generally cannot install a processor supporting SpeedStep/PowerNow!/LongRun technology into an older system that was originally equipped with a processor that did not support that technology.

Systems running Windows 9x/Me or NT/2000 require a special configuration utility or driver to control the processor performance settings. Because the driver must be configured to the specific laptop motherboard, it is available only from the manufacturer or vendor of a given system. Typically, the driver automatically switches processor performance modes when the power source changes from AC to battery power. Normally, the driver displays an indicator (usually a small flag) in the notification area or system tray of the Windows taskbar indicating in which mode the CPU is currently running. The driver also typically adds a processor performance-control tab to the Power Management tool in the Control Panel. By clicking on the indicator in the system tray, you can switch among Maximum Performance, Automatic (dynamically switchable), or Battery Optimized modes on demand. By using the Control tab added to the Power Management tool, you can select options allowing you to disable the processor performance-control technology, add or remove the icon from the taskbar, and enable or disable audio notification when performance changes.

Windows XP includes native support for processor performance-control technologies such as SpeedStep, PowerNow!, and LongRun, which means that manufacturer-supplied drivers are no longer necessary. This native support also includes an algorithm that dynamically balances system performance and power consumption, based on the current CPU workload and remaining battery life. Windows XP uses four specific processor policies (modes of operation) to control processor performance. The processor policies used by Windows XP are shown in below table in order of power consumption from highest to lowest.

Power Scheme	Processor Policy (AC Power)	Processor Policy (Battery Power)
Always On	None	None
Home/Office Desk	None	Adaptive
Minimal Power Management	Adaptive	Adaptive
Portable/Laptop	Adaptive	Adaptive
Presentation	Adaptive	Degrade
Max Battery	Adaptive	Degrade