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CPUs (Central processing units) in their various incarnations consume some amount of electric power. more...
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This power is dissipated both by the action of the switching devices contained in the CPU (such as transistors or vacuum tubes) as well as energy lost in the form of heat due to the resistivity of the electrical circuits. This is a major consideration in the design of CPUs and the computers they are used in.
Some implementations of CPUs use very little power. For example, the CPUs in mobile phones and pacemakers often use just a few microwatts. On the other hand, CPUs in general purpose microcomputers dissipate significantly more power because of their higher complexity and speed. These microelectronic CPUs may consume power in the order of several watts. Historically, early CPUs implemented with vacuum tubes consumed power in the order of many kilowatts (103 watts).
CPUs for desktop computers typically use more power than any other component inside the computer, except perhaps recent technology video cards which contain special purpose CPUs themselves. 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, the typical thermal power, which is measured under normal load, and the maximum thermal power, which is measured under a worst-case set of instructions. For example, the Pentium 4 2.8 GHz has 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power.
There are some engineering reasons for this pattern.
Performing at higher speed always requires higher power. Reducing processor speed when possible saves power.;
New features generally require more transistors, each of which uses power. Turning unused areas off saves power.;
As a processor model's design matures, smaller transistors, lower-voltage structures, and design experience reduce power consumption.;
Early CPUs
Note that these figures include power dissipation due to energy lost by the computer's power supply and some minor peripherals. However, since the CPU component of these early computers easily accounted for most of the computer's power dissipation, they are mentioned here:
Read more at Wikipedia.org
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