Some CPUs include more than one voltage rail: e.g., an I/O voltage and a CPU core voltage rail. Some of the CPU core voltage rails have a range over which they can operate and the choice impacts the available frequency of operation of the core. For example GTL can operate anywhere from about 1.2 V down to something like 0.3 or 0.4 V. Some CPUs are designed to allow their power supply to be programmed by the BIOS (or other means) to select the desired operating core voltage. There is always both a static part (not affected by freq) and a dynamic part (affected by freq) to the dissipation.
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