Overvolting
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Overvolting is the practice of increasing the voltage applied to computer components. It is sometimes used to increase the stability or operating frequency achievable when overclocking.
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[edit] Background
MOSFET-based digital circuits operate using voltages at circuit nodes to represent logical state. The voltage at these nodes switches between a high voltage and a low voltage during normal operation—when the inputs to a logic gate transition, the transistors making up that gate may toggle the gate's output.
At each node in a circuit is a certain amount of capacitance. Capacitance can be thought of as a measure of how long it takes for a given current to effect a given voltage change. The capacitance arises from various sources, mainly transistors (primarily gate capacitance and diffusion capacitance) and wires (coupling capacitance). Toggling a voltage at a circuit node requires charging or discharging the capacitance at that node; since currents are related to voltage, the time it takes depends on the voltage applied. By applying a higher voltage to the devices in a circuit, the capacitances are charged and discharged more quickly, resulting in faster operation of the circuit and allowing for higher frequency operation.
[edit] Caveats
The primary caveat of overvolting is increased heat: the power dissipated by a circuit increases with the square of the voltage applied, so even small voltage increases significantly affect power. At higher temperatures, transistor performance is adversely affected, and at some threshold, the performance reduction due to the heat exceeds the potential gains from the higher voltages. Overheating and damage to circuits can occur very quickly when using high voltages.
There are also longer-term concerns: various adverse device-level effects such as hot carrier injection and electromigration occur more rapidly at higher voltages, decreasing the lifespan of overvolted components.
[edit] Voltage Modifications
Many modern components allow voltage regulation to be controlled through software (for example, through the BIOS or using applications such as PowerStrip [1]). It is usually possible to control the voltages supplied to the CPU, RAM, PCI, and PCI Express (or AGP) port through a PC's BIOS.
However, some components do not allow software control of supply voltages, and hardware modification is required by overclockers seeking to overvolt the component for extreme overclocks. Video cards and motherboard northbridges are components which frequently require hardware modifications to change supply voltages.
These modifications are known as "voltage mods" in the overclocking community.
