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This paper describes the embedded feedback and control system on a 90-nm Itanium family processor, code-named Montecito, that maximizes performance while staying within a target power and temperature (PT) envelope. This system, referred to as Foxton Technology (FT), utilizes on-chip sensors and an embedded microcontroller to measure PT and modulate both voltage and frequency (VF) to optimize performance while meeting PT constraints. Changing both VF takes advantage of the cubic relationship of P∝CV2F. We present measured results that show a 31% reduction in power for only a 10% drop in frequency. Montecito is able to implement FT using only 0.5% of the die area and 0.5% of the die power.