Increasing this speed (overclocking) is done using CMOS Setup by adjusting the CPU Speed or Advanced Chipset Features properties. Increasing the clock speed requires more power and generates more heat. Therefore, an overclocked system must have a suitable power supply and sufficient cooling. The operating environment (the warmth of the room and build-up of dust) must also be quite carefully controlled.
Overclocking is generally performed by hobbyist and games enthusiasts but it is also a means to build a PC more cheaply by specifying lower cost components then boosting their performance.
Without cooling, overclocking increases the risk of thermal damage to components and may increase the frequency of system lockup. It also invalidate the warranty. Vendors generally try to prevent overclocking by disabling custom setting in the computer's CMOS Setup program.
A CPU may also run at a lower actual speed than it is capable of if it is put in a power saving mode.
Power Management (Throttling)
Rising energy costs and environmental legislation are placing power efficiency at the top of the agenda for IT buyers. In terms of CPU performance, more speed means greater power consumption and heat production. To deal with these issues, CPUs can implement power management to enter lower power states, referred to as throttling.
Intel chips implement throttling using speed step technology. The original version simply allowed high and low frequency modes. Enhanced Speed Step allows the CPU to step up or down through a range of voltages.
Another aspect of power management is protection the CPU. If a processor runs too hot, the system can become unstable or damage can occur. Some Intel CPUs provide Thermal Monitor (TM) modes, triggered by a temperature gauge (the activation point depends on the processor, but tends to be around 50-65 c). Intel CPUs work in one of two modes, depending on the age of the model:
-TM1 (speed step) - the CPU inserts idle cycles between instructions (implemented on early Pentium 4 models).
-TM2 (Enhanced speed step) - the CPU lowers the actual clock speed (used on later P4s and current mobile and desktop CPUs).
Power management on AMD CPUs is referred to as Power Now! (mobile CPUs) or Cool in Quiet (desktop CPUs).