PStates

P-states, short for processor performance states, are a hardware-supported mechanism on many x86 CPUs to adjust operating frequency and core voltage to balance performance and power consumption. They complement C-states, which are idle power-down modes. In P-states, the processor can operate at several discrete performance levels, commonly labeled P0 as the highest performance state, with progressively lower states (P1, P2, etc.). Higher-numbered states reduce clock speed and require lower voltage, saving power and producing less heat. The exact number and characteristics of P-states vary by microarchitecture.

Dynamic voltage and frequency scaling (DVFS) is the mechanism that enables P-states to be switched on the fly. Intel technologies such as Enhanced SpeedStep (EIST) enable the CPU to transition between P-states. AMD uses similar mechanisms under different branding (for example, PowerNow! or Cool'n'Quiet). Turbo or boost features may temporarily raise frequencies beyond the nominal P0 state, but turbo is a related capability rather than a separate P-state.

Software controls: Operating systems provide interfaces to manage P-states via CPU frequency scaling. In Linux, the cpufreq subsystem offers governors (performance, powersave, ondemand, schedutil) to select P-states; Windows uses power plans to influence processor performance states. Firmware and platform firmware may also define P-state tables at boot, shaping the available options.

Effects and considerations: Enabling P-states can improve battery life and reduce heat on portable devices, while allowing higher performance when needed. Support and behavior vary by CPU model and motherboard. Misconfiguration or aggressive scaling can cause performance hiccups or instability in some scenarios. P-states are a key part of modern power management alongside other mechanisms such as C-states and Turbo Boost. See also CPU frequency scaling, DVFS, EIST, C-states, and Turbo Boost.