CPUs in other electronics often use far less power. For example, the CPUs in mobile phones or pacemakers use just a few microwatts. CPUs in personal computers use a lot of power because the manufacturers are rewarded for raw speed instead of energy efficiency. This top-performance speed requires significantly more power in the cases of most (but not all) CPU architectures. One of the simplest way to reduce the power consumption of a PC's CPU is just to slow its clock rate.
CPUs for desktop computers typically use more power than any other component inside the computer. The steady trend in CPU power supplies over the past decade has been towards using lower voltages and having considerably higher currents. While energy-saving features have been instituted in PCs for when they are idle, the overall consumption of today's high-drain CPUs is considerable. This is in strong contrast with the much lower energy consumption of CPUs designed for low-power environments. One such CPU, the Intel XScale, can run at 600 MHz with only half a watt of power, whereas x86 PC processors from Intel in the same performance bracket consume roughly eighty times as much energy.
Processor manufacturers usually release two power consumption numbers for a CPU, first is the 'typical' thermal power, which is how much power the CPU draws under normal load, and the other is the maximum thermal power, which is how much power it can draw if you give it a worst-case set of instructions. As an example, the Pentium 4 2.8GHz has a typical thermal power of 68.4 W, but a maximum thermal power of 85 W. When the CPU is idle, it will draw far less than the typical thermal power. Manufactureres generally don't release the idle thermal-power statistics for desktop chips.
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