Processor 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 by both the action of the switching devices contained in the CPU, such as transistors or vacuum tubes, and via 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, a special type of CPU. 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]}.

Processor manufacturers usually release two power consumption numbers for a CPU, the typical thermal power, which is measured under normal load, and the maximum thermal power, which is measured under a worst-case set of instructions. 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), the maximum amount of power the cooling system in a computer is required to dissipate. Some CPUs, such as newer Intel-CPUs, have the typical power consumption defined as TDP and some, like CPUs from Advanced Micro Devices (AMD), have the maximum power consumption defined as TDP.

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.

References

Weik, Martin H. (1955). "A Survey of Domestic Electronic Digital Computing Systems". United States Department of Commerce Office of Technical Services. {{cite journal}}: Cite journal requires |journal= (help)
http://developer.intel.com/design/itanium2/documentation.htm#datasheets
http://www.intel.com/pressroom/kits/quickreffam.htm
http://www.intel.com/design/mobile/datashts/24297301.pdf
http://www.intel.com/design/intarch/prodbref/27331106.pdf
http://www.via.com.tw/en/products/processors/c7-d/
http://mbsg.intel.com/mbsg/glossary.aspx
http://download.intel.com/design/Xeon/datashts/25213506.pdf

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.

See also

References

External links