| Experiments Home |
|
| Computers |
|
|
| Underclocking |
|
|
|
|
|
|
Underclocking Projects & Experiments
Underclocking See also ovreclocking Underclocking (sometimes downclocking) is the practice of modifying a microprocessor's speed settings to run at a lower clock speed than the manufacturer's specification. The purpose is generally to decrease the need for heat dissipation devices or decrease the electrical power consumption. This can provide increased system stability in high-heat environments, or can allow a system to run with a lower airflow (and therefore quieter) 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 the opposite of overclocking.
When usedAutomatic 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) will also underclock themselves automatically when under a light processing load. Some processors underclock automatically as a defensive measure, to prevent overheating which could cause permanent damage. When such a processor reaches a temperature level deemed too high for safe operation, the thermal control circuit activates, automatically decreasing the clock and CPU core voltage until the temperature has returned to a safe level. In a properly cooled environment, this mechanism should trigger rarely (if ever). In addition, other components can also be underclocked such as the videocard or RAM. This is primarily done when the components are experiencing stability problems running at their rated frequency specification. There are several different underclocking competitions similar in format to overclocking competitions, except the goal is to have the lowest clocked computer as opposed to the highest. Advantages
Disadvantages
In practiceLinuxThe 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 speed. The kernel includes five governors by default: conservative, ondemand, performance, powersave, and userspace. The conservative and ondemand governors adjust the clock speed 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 speed statically: performance to the highest available, powersave to the lowest available, and userspace to a frequency determined and controlled by the user. WindowsUnderclocking can be done manually in the BIOS or with Windows applications, or dynamically using technologies such as Intel's SpeedStep or AMD's Cool'n'Quiet. Apple TVA 1.0 GHz Intel Pentium-M based chip (codenamed "Crofton") with 2MB of L2 cache, underclocked to 350MHz bus, runs the Apple TV. PerformanceThe 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 speed. Generally speaking, the lower the speed of a CPU, the closer it's speed will be to that of the bus, and the less time it spends waiting. See also
External links
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia Encyclopedia article "Underclocking" |
