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"Underclocking" also known as "Downclocking" is the practice of modifying a synchronous circuit's timing settings to run at a lower clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
 than the manufacturer's specification. "Underclocking" is the opposite of "overclocking
Overclocking

Overclocking is the process of running a computer hardware at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by personal computer enthusiasts seeking an increase in the performance of their computers....
."

microprocessors, the purpose is generally to decrease the need for heat dissipation devices
Computer cooling

Computer cooling is the process of removing heat from computer components.A computer system's components produce large amounts of heat during operation, including integrated circuits such as Central processing units, chipset and Video card, along with Hard disk drive....
 or decrease the electrical power consumption
CPU power dissipation

CPU power dissipation or Central processing unit power dissipation is the process in which Central processing units consume electrical energy, and dissipate this energy by both the action of the switching devices contained in the CPU and via the energy lost in the form of heat due to the resistivity of the electrical circuits....
. This can provide increased system stability in high-heat environments, or can allow a system to run with a lower airflow (and therefore quieter
Quiet PC

A quiet PC is a personal computer that makes little noise. Common uses for quiet PCs include video editing, sound mixing, home servers, and home theater PCs....
) cooling fan or without one at all.






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"Underclocking" also known as "Downclocking" is the practice of modifying a synchronous circuit's timing settings to run at a lower clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
 than the manufacturer's specification. "Underclocking" is the opposite of "overclocking
Overclocking

Overclocking is the process of running a computer hardware at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by personal computer enthusiasts seeking an increase in the performance of their computers....
."

Microprocessor "underclocking"

For microprocessors, the purpose is generally to decrease the need for heat dissipation devices
Computer cooling

Computer cooling is the process of removing heat from computer components.A computer system's components produce large amounts of heat during operation, including integrated circuits such as Central processing units, chipset and Video card, along with Hard disk drive....
 or decrease the electrical power consumption
CPU power dissipation

CPU power dissipation or Central processing unit power dissipation is the process in which Central processing units consume electrical energy, and dissipate this energy by both the action of the switching devices contained in the CPU and via the energy lost in the form of heat due to the resistivity of the electrical circuits....
. This can provide increased system stability in high-heat environments, or can allow a system to run with a lower airflow (and therefore quieter
Quiet PC

A quiet PC is a personal computer that makes little noise. Common uses for quiet PCs include video editing, sound mixing, home servers, and home theater PCs....
) cooling fan or without one at all. For example, a Pentium 4 processor clocked at 2.4 GHz can be "underclocked" to 1.8 GHz and can then be safely run with reduced fan speeds. However, this invariably comes at the expense of some system performance. "Underclocking" is also sometimes used to monitor closely a process for its behavior at lower performance where a fast performance running of the process does not allow that; it allows a programmer or technician to troubleshoot an application that is running abnormally quickly. "Underclocking" can also be performed on graphics card processors (GPUs), usually with the aim of reducing heat output. For instance, it is possible to set a GPU to run at lower clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
s when performing everyday tasks (e.g. internet browsing), thus allowing the card to operate at lower temperature and thus lower, quieter fan speeds. The GPU can then be overclocked for more graphically intense applications, such as games. "Underclocking" a GPU will reduce performance, but this decrease will probably not be noticeable except in graphically intensive applications.

Memory "underclocking"

Newer and faster RAM
Ram

Ram, ram, or RAM as a non-acronymic wordAs a non-acronymic word Ram, ram, or RAM may refer to:...
 may be "underclocked" to match older systems as an inexpensive way to replace rare or discontinued memory. This might also be necessary if stability problems are encountered at higher settings.

When used

Dynamic frequency scaling
Dynamic frequency scaling

Dynamic frequency scaling is a technique in computer architecture where a processor is run at a less-than-maximum Clock rate in order to power management....
 (automatic "underclocking") is very common on laptop computers and is beginning to emerge on desktop computers as well. In laptops, the processor is usually "underclocked" automatically whenever the computer is operating on batteries. Most newer notebook and some desktop processors (see Cool'n'Quiet
Cool'n'Quiet

Cool'n'Quiet is a central processing unit CPU throttling and power saving technology introduced by AMD with their Athlon 64 processor line. It works by reducing the processor's clock rate and voltage when the processor is idle....
) will also underclock themselves automatically when under a light processing load. Intel has also used this method on their Core 2 Duo processors, through a feature called SpeedStep
SpeedStep

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....
.

Some processors "underclock" automatically as a defensive measure, to prevent overheating which could cause permanent damage. When such a processor reaches a temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 level deemed too high for safe operation, the thermal control circuit activates, automatically decreasing the clock and CPU core voltage
CPU core voltage

The CPU core voltage is the power supply voltage supplied to the central processing unit , Graphics processing unit, or other device containing a processing core....
 until the temperature has returned to a safe level. In a properly cooled environment, this mechanism should trigger rarely (if ever).

There are several different "underclocking" competitions similar in format to overclocking
Overclocking

Overclocking is the process of running a computer hardware at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by personal computer enthusiasts seeking an increase in the performance of their computers....
 competitions, except the goal is to have the lowest clocked computer, as opposed to the highest.

Advantages

  • Reduced heat generation.
  • Reduced electrical power consumption.
  • Longer hardware lifespan.
  • Increased stability.
  • Increased battery life.
  • Reduced noise from cooling parts due to reduced heat dissipation requirements.


In practice


Linux

The Linux kernel, as well as other open-source kernels, include a feature known as CPU frequency modulation. This feature, often known as cpufreq, gives the system administrator a variable level of control over the CPU's clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
. The kernel includes five governors by default: conservative, Ondemand, Performance, Powersave, and Userspace. The conservative and Ondemand governors adjust the clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
 depending on the CPU load, but each with different algorithms. The Ondemand governor jumps to maximum frequency on CPU load and decreases the frequency step by step on CPU idle, whereas the conservative governor increases the frequency step by step on CPU load and jumps to lowest frequency on CPU idle. The performance, Powersave and Userspace governors set the clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
 statically: performance to the highest available, Powersave to the lowest available, and Userspace to a frequency determined and controlled by the user.

Windows

"Underclocking" can be done manually in the BIOS
BIOS

In computing, the Basic Input/Output System , also known as the System BIOS, is a de facto standard defining a firmware interface for IBM PC Compatible computers....
 or with Windows
Microsoft Windows

Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces ....
 applications, or dynamically using features such as Intel's SpeedStep
SpeedStep

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....
 or AMD's Cool'n'Quiet
Cool'n'Quiet

Cool'n'Quiet is a central processing unit CPU throttling and power saving technology introduced by AMD with their Athlon 64 processor line. It works by reducing the processor's clock rate and voltage when the processor is idle....
.

Asus Eee PC
ASUS Eee PC

The ASUS Eee PC is a subnotebook / netbook computer by ASUS and a part of ASUS Eee product family. At the time of its introduction in fall 2007, it was noted for its combination of a light weight, Linux operating system, solid-state drive and relatively low cost....

Some versions of the Eee PC uses a 900 MHz Intel Celeron
Celeron

The Celeron brand is a range of x86 CPUs from Intel targeted at budget/value personal computers?with the motto, "delivering great quality at an exceptional value"....
 M processor underclocked to 630 MHz.

Apple iPhone

Apple's iPhone
IPhone

The iPhone is an internet-connected multimedia smartphone designed and marketed by Apple Inc. with a flush multi-touch screen and a minimal hardware interface....
 and iPhone 3G use the "underclocking" of a more powerful processor, rather than the full clocking of a less powerful processor, to maximize battery life. The power consumed by using a slower processor is more than using the more powerful processor at a lower clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
. In this application, the ARM
Arm

In anatomy, an arm is one of the upper limbs of an animal. The term arm can also be used for analogous structures, such as one of the paired upper limbs of a four-legged animal, or the cephalopod arm....
 1176 processor is "underclocked" from 620 MHz to 412 MHz.

Performance

The performance of an "underclocked" machine will often be better than might be expected. Under normal desktop use, the full power of the CPU is rarely needed. Even when the system is busy, a large amount of time is usually spent waiting for data from memory, disk, or other devices. Such devices communicate with the CPU through a bus which operates at a much lower bandwidth. Generally speaking, the lower the clock rate
Clock rate

The clock rate is the fundamental rate in cycles per second for the frequency of the clock in any synchronous circuit. For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wav...
 of a CPU, the closer its performance will be to that of the bus, and the less power it spends waiting.

See also

  • SpeedStep
    SpeedStep

    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....
  • Cool'n'Quiet
    Cool'n'Quiet

    Cool'n'Quiet is a central processing unit CPU throttling and power saving technology introduced by AMD with their Athlon 64 processor line. It works by reducing the processor's clock rate and voltage when the processor is idle....
  • Undervolting
  • Crystal CPUID - a tool that uses Cool'n'Quiet to set custom clock/voltage step settings

External links