A voltage regulator module or VRM, sometimes called PPM (processor power module), is a buck converter that provides a microprocessor the appropriate supply voltage, converting +5 V or +12 V to a much lower voltage required by the CPU. Some are soldered to the motherboard while others are installed in an open slot. It allows processors with different supply voltage to be mounted on the same motherboard. Most modern CPUs require less than 1.5 V. CPU designers tend to design to smaller CPU core voltages; lower voltages help reduce CPU power dissipation, often referred to as thermal design power (TDP).
Some voltage regulators provide a fixed supply voltage to the processor, but most of them sense the required supply voltage from the processor, essentially acting as a continuously-variable adjustable regulator. In particular, VRMs that are soldered to the motherboard are supposed to do the sensing, according to the Intel specification.
Modern graphics processing units (GPU) also use a VRM due to higher power and current requirements.
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