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Processor Power Supply Levels

Beginning with the Pentium MMX, Intel adopted dual voltage-supply levels for the overall IC and for its core. This was done for two reasons:

  • To make the processor's switching time faster so that it can be clocked faster.
  • To reduce the processor's power consumption/dissipation (in the form of heat).

Common Intel external/internal voltage supplies are +5/+5 for older units and +3.3/+3.3, +3.3/+2.8, +3.3/+1.8, and +3.3/1.45 for newer units.

The transistors that make up the microprocessor (and every other digital device) have maximum turn on and turn off rates. When the system clock nears this point, no further performance increase can occur without a change that allows the transistor to be clocked faster. The answer was to move the core's high and low logic voltage levels (that represent 1 and 0) closer to each other (0 and 1.8 vs. 0 and 5) so that it requires less time to switch back and forth between them. At the maximum change rate of the transistors, it doesn't take as long to get from 0 to 1.8V as it does to get from 0 to 5.0V. Therefore, you can turn the devices on and off more often with a smaller voltage separation.

The second reason for using the lower voltage level in the processor core is also electrical—transistors dissipate power in the form of heat. In electronic devices, power dissipation is directly proportional to both voltage and current. Therefore, if the current or the voltage associated with an electronic component like a transistor is lowered, so is the level of power that will be generated. Although the power associated with a single microprocessor is very small, when you multiply that value by millions of transistors, you get a very large number.

Clone processors may use compatible voltages (especially if they are pin compatible) or may use completely different voltage levels. Common voltages for clone microprocessors include +5, +3.3, +2.5, and +2.2. The additional voltage levels are typically generated through special regulator circuits on the system board that you might have to set manually. In each case, the system board user's guide should be consulted anytime the microprocessor is replaced or upgraded.

From the second-generation Pentiums forward, system boards have employed Voltage Regulator Modules (VRMs) to supply special voltage levels associated with different types of microprocessors that might be installed. The VRM module may be designed as a plug-in module so that it can be replaced easily in case of component failure. This is a somewhat common occurrence with voltage regulator devices. It also enables the system board to be upgraded when a new Pentium device is developed that requires a different voltage level or a different voltage pairing.

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