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Processor power dissipation or processing unit power dissipation is the process in which computer processors consume
electrical energy Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and electr ...
, and dissipate this energy in the form of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
due to the
resistance Resistance may refer to: Arts, entertainment, and media Comics * Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm: ** ''Resistance'' (comics), based on the video game of the same title ** ''T ...
in the
electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electri ...
s.


Power management

Designing CPUs that perform tasks efficiently without overheating is a major consideration of nearly all CPU manufacturers to date. Historically, early CPUs implemented with
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
s consumed power on the order of many
kilowatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after Jame ...
s. Current CPUs in general-purpose
personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tech ...
s, such as desktops and laptops, consume power in the order of tens to hundreds of watts. Some other CPU implementations use very little power; for example, the CPUs in
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...
s often use just a few
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s of electricity, while some
microcontroller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs ( processor cores) along with memory and programma ...
s used in
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' ...
s may consume only a few milliwatts or even as little as a few microwatts. There are a number of engineering reasons for this pattern: * For a given CPU core, energy usage will scale up as its clock rate increases. Reducing the clock rate or
undervolting Dynamic voltage scaling is a power management technique in computer architecture, where the voltage used in a component is increased or decreased, depending upon circumstances. Dynamic voltage scaling to increase voltage is known as overvolting; d ...
usually reduces energy consumption; it is also possible to undervolt the microprocessor while keeping the clock rate the same. * New features generally require more
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
s, 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 (for instance, AMD's average CPU power) * ''maximum thermal power'', which is measured under a worst-case load For example, the Pentium 4 2.8 GHz has a 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.
Datasheet A datasheet, data sheet, or spec sheet is a document that summarizes the performance and other characteristics of a product, machine, component (e.g., an electronic component), material, subsystem (e.g., a power supply), or software in suffici ...
s normally contain the
thermal design power The thermal design power (TDP), sometimes called thermal design point, is the maximum amount of heat generated by a computer chip or component (often a CPU, GPU or system on a chip) that the cooling system in a computer is designed to dissipa ...
(TDP), which is the maximum amount of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
generated by the CPU, which the cooling system in a computer is required to dissipate. Both Intel and
Advanced Micro Devices Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufa ...
(AMD) have defined TDP as the maximum heat generation for thermally significant periods, while running worst-case non-synthetic workloads; thus, TDP is not reflecting the actual maximum power of the processor. This ensures the computer will be able to handle essentially all applications without exceeding its thermal envelope, or requiring a cooling system for the maximum theoretical power (which would cost more but in favor of extra headroom for processing power). In many applications, the CPU and other components are idle much of the time, so idle power contributes significantly to overall system power usage. When the CPU uses
power management Power management is a feature of some electrical appliances, especially copiers, computers, computer CPUs, computer GPUs and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power ...
features to reduce energy use, other components, such as the motherboard and chipset, take up a larger proportion of the computer's energy. In applications where the computer is often heavily loaded, such as scientific computing, performance per watt (how much computing the CPU does per unit of energy) becomes more significant. CPUs typically use a significant portion of the power consumed by the computer. Other major uses include fast
video card A graphics card (also called a video card, display card, graphics adapter, VGA card/VGA, video adapter, display adapter, or mistakenly GPU) is an expansion card which generates a feed of output images to a display device, such as a computer mo ...
s, which contain
graphics processing unit A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mo ...
s, and
power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...
. In laptops, the
LCD A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...
's backlight also uses a significant portion of overall power. While energy-saving features have been instituted in personal computers for when they are idle, the overall consumption of today's high-performance CPUs is considerable. This is in strong contrast with the much lower energy consumption of CPUs designed for low-power devices.


Sources

There are several factors contributing to the CPU power consumption; they include dynamic power consumption, short-circuit power consumption, and power loss due to
transistor leakage current In electronics, leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow of cu ...
s: The dynamic power consumption originates from the activity of logic gates inside a CPU. When the logic gates toggle, energy is flowing as the capacitors inside them are charged and discharged. The dynamic power consumed by a CPU is approximately proportional to the CPU frequency, and to the square of the CPU voltage: where is the switched load capacitance, is frequency, is voltage. When logic gates toggle, some transistors inside may change states. As this takes a finite amount of time, it may happen that for a very brief amount of time some transistors are conducting simultaneously. A direct path between the source and ground then results in some short-circuit power loss (P_). The magnitude of this power is dependent on the logic gate, and is rather complex to model on a macro level. Power consumption due to leakage power (P_) emanates at a micro-level in transistors. Small amounts of currents are always flowing between the differently doped parts of the transistor. The magnitude of these currents depend on the state of the transistor, its dimensions, physical properties and sometimes temperature. The total amount of leakage currents tends to inflate for increasing temperature and decreasing transistor sizes. Both dynamic and short-circuit power consumption are dependent on the clock frequency, while the leakage current is dependent on the CPU supply voltage. It has been shown that the energy consumption of a program shows convex energy behavior, meaning that there exists an optimal CPU frequency at which energy consumption is minimal for the work done.


Reduction

Power consumption can be reduced in several ways, including the following: * Voltage reduction
dual-voltage CPU The CPU core voltage (''VCORE'') is the power supply voltage supplied to the CPU (which is a digital circuit), GPU, or other device containing a processing core. The amount of power a CPU uses, and thus the amount of heat it dissipates, is the prod ...
s,
dynamic voltage scaling Dynamic voltage scaling is a power management technique in computer architecture, where the voltage used in a component is increased or decreased, depending upon circumstances. Dynamic voltage scaling to increase voltage is known as overvolting; ...
,
undervolting Dynamic voltage scaling is a power management technique in computer architecture, where the voltage used in a component is increased or decreased, depending upon circumstances. Dynamic voltage scaling to increase voltage is known as overvolting; d ...
, etc. * Frequency reduction
underclocking Underclocking, also known as downclocking, is modifying a computer or electronic circuit's timing settings to run at a lower clock rate than is specified. Underclocking is used to reduce a computer's power consumption, increase battery life, redu ...
,
dynamic frequency scaling Dynamic frequency scaling (also known as CPU throttling) is a power management technique in computer architecture whereby the frequency of a microprocessor can be automatically adjusted "on the fly" depending on the actual needs, to conserve ...
, etc. * Capacitance reduction increasingly integrated circuits that replace PCB traces between two chips with relatively lower-capacitance on-chip metal interconnect between two sections of a single integrated chip;
low-κ dielectric In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant (κ, kappa) relative to silicon dioxide. Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of micr ...
, etc. * Power gating techniques such as clock gating and globally asynchronous locally synchronous, which can be thought of as reducing the capacitance switched on each clock tick, or can be thought of as locally reducing the clock frequency in some sections of the chip. * Various techniques to reduce the switching activity number of transitions the CPU drives into off-chip data buses, such as non-multiplexed
address bus In computer architecture, a bus (shortened form of the Latin ''omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ex ...
, bus encoding such as
Gray code addressing The reflected binary code (RBC), also known as reflected binary (RB) or Gray code after Frank Gray, is an ordering of the binary numeral system such that two successive values differ in only one bit (binary digit). For example, the representat ...
, or
value cache encoding Power consumption is becoming increasingly important for both embedded, mobile computing and high-performance systems.Power Protocol: Reducing Power Dissipation on Off-Chip Data Buses http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=117626 ...
such as power protocol. Sometimes an "activity factor" (''A'') is put into the above equation to reflect activity. * Sacrificing transistor density for higher frequencies. * Layering heat-conduction zones within the CPU framework ("Christmassing the Gate"). * Recycling at least some of that energy stored in the capacitors (rather than dissipating it as heat in transistors)
adiabatic circuit Adiabatic circuits are low-power electronic circuits which use " reversible logic" to conserve energy. The term " adiabatic" refers to an ideal thermodynamic process in which no heat or mass is exchanged with the surrounding environment, allud ...
, energy recovery logic, etc. * Optimizing machine code - by implementing compiler optimizations that
schedules A schedule or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such things are i ...
clusters of instructions using common components, the CPU power used to run an application can be significantly reduced.


Clock frequencies and multi-core chip designs

Historically, processor manufacturers consistently delivered increases in
clock rate In computing, the clock rate or clock speed typically refers to the frequency at which the clock generator of a processor can generate pulses, which are used to synchronize the operations of its components, and is used as an indicator of the ...
s and instruction-level parallelism, so that single-threaded code executed faster on newer processors with no modification. More recently, in order to manage CPU power dissipation, processor makers favor
multi-core A multi-core processor is a microprocessor on a single integrated circuit with two or more separate processing units, called cores, each of which reads and executes program instructions. The instructions are ordinary CPU instructions (such ...
chip designs, thus software needs to be written in a multi-threaded or multi-process manner to take full advantage of such hardware. Many multi-threaded development paradigms introduce overhead, and will not see a linear increase in speed when compared to the number of processors. This is particularly true while accessing shared or dependent resources, due to lock contention. This effect becomes more noticeable as the number of processors increases. Recently, IBM has been exploring ways to distribute computing power more efficiently by mimicking the distributional properties of the human brain.


Processor overheating

Processor can be damaged from overheating, but vendors protect processors with operational safeguards such as throttling and automatic shutdown. When a core exceeds the set throttle temperature, processors can reduce power to maintain a safe temperature level and if the processor is unable to maintain a safe operating temperature through throttling actions, it will automatically shut down to prevent permanent damage.


See also

*
Autonomous peripheral operation In computing, autonomous peripheral operation is a hardware feature found in some microcontroller architectures to off-load certain tasks into embedded autonomous peripherals in order to minimize latencies and improve throughput in hard real-t ...
*
Advanced Configuration and Power Interface Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto c ...
(ACPI) *
Glitch removal Glitch removal is the elimination of glitchesunnecessary signal transitions without functionalityfrom electronic circuits. Power dissipation of a gate occurs in two ways: static power dissipation and dynamic power dissipation. Glitch power comes ...
* Green computing * IT energy management * List of CPU power dissipation *
Low-power electronics Low-power electronics are electronics, such as notebook processors, that have been designed to use less electric power than usual, often at some expense. In the case of notebook processors, this expense is processing power; notebook processors us ...
*
Moore's law Moore's law is the observation that the number of transistors in a dense integrated circuit (IC) doubles about every two years. Moore's law is an observation and projection of a historical trend. Rather than a law of physics, it is an empi ...
*
Overclocking In computing, overclocking is the practice of increasing the clock rate of a computer to exceed that certified by the manufacturer. Commonly, operating voltage is also increased to maintain a component's operational stability at accelerated spe ...
* Performance per watt * Power analysis * Power dissipation *
PowerTOP PowerTOP is a software utility designed to measure, explain and minimise a computer's electrical power consumption. It was released by Intel in 2007 under the GPLv2 license. It works for Intel, AMD, ARM and UltraSPARC processors. PowerTOP anal ...


References


Further reading

* * 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/ * https://web.archive.org/web/20090216190358/http://mbsg.intel.com/mbsg/glossary.aspx * http://download.intel.com/design/Xeon/datashts/25213506.pdf * http://www.intel.com/Assets/en_US/PDF/datasheet/313079.pdf, page 12 * http://support.amd.com/us/Processor_TechDocs/43374.pdf, pages 10 and 80.


External links


CPU Reference for all vendors. Process node, die size, speed, power, instruction set, etc.



SizingLounge
{snd online calculation tool for server energy costs
For specification on Intel processors

Making x86 Run Cool
2001-04-15, by Paul DeMone Central processing unit Electric power