CPU power dissipation

Central processing unit power dissipation or CPU power dissipation is the process in which central processing units (CPUs) consume electrical energy, and dissipate this energy both by the action of the switching devices contained in the CPU (such as transistors or vacuum tubes) and by the energy lost in the form of heat due to the impedance of the electronic circuits. Designing CPUs that perform these tasks efficiently without overheating is a major consideration in nearly all CPU manufacturers to date.

Some implementations of CPUs use very little power, for example, the CPUs in mobile phones often use just a few hundred milliwatts of electricity. In comparison, CPUs in general purpose personal computers, such desktops and laptops, dissipate significantly more power because of their higher complexity and speed. These microelectronic CPUs may consume power in the order of tens of watts. Historically, early CPUs implemented with vacuum tubes consumed power in the order of many kilowatts.

CPUs for desktop computers typically use more power than any other component inside the computer, except perhaps recent video cards which contain graphics processing units. While energy-saving features have been instituted in personal computers for when they are idle, the overall consumption of today's high-drain CPUs is considerable. This is in strong contrast with the much lower energy consumption of CPUs designed for low-power environments. One such CPU, the Intel XScale, can run at 600 MHz with only half a watt of power, whereas x86 PC processors from Intel in the same performance bracket consume roughly eighty times as much energy.^{[citation needed]}

There are some engineering reasons for this pattern.

• For a given device, operating at a higher clock rate always requires more power. Reducing the clock rate of the microprocessor through power management when possible reduces energy consumption.
• New features generally require more transistors, each of which uses power. Turning unused areas off saves energy, such as through clock gating.
• As a processor model's design matures, smaller transistors, lower-voltage structures, and design experience may reduce energy consumption.

Processor manufacturers usually release two power consumption numbers for a CPU:

• typical thermal power, which is measured under normal load.
• maximum thermal power, which is measured under a worst-case load.

For example, the Pentium 4 2.8 GHz has 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power.

Datasheets normally contain the thermal design power (TDP), which is the maximum amount of power the cooling system in a computer is required to dissipate. Both Intel and Advanced Micro Devices (AMD) have defined TDP as the maximum power consumption for thermally significant periods running worst-case non-synthetic workloads. Thus, TDP is not the actual maximum power of the processor.

[edit] See also

• List of CPU power dissipation
• Power management
• Advanced Configuration and Power Interface
• Low-power electronics
• Voltage and frequency scaling
• Overvolting
• Undervolting
• Overclocking
• Underclocking
• Average CPU power

[edit] References

[edit] External links

• CPU Reference for all vendors. Process node, die size, speed, power, instruction set, etc.
• Processor Electrical Specifications
• SizingLounge – Online calculation tool for server energy costs.
• For specification on Intel processors.