The Thermal Control Circuit (Intel) or Hardware Thermal Control (AMD) is a feature of x86 microprocessors which throttles the processor when it reaches a critical temperature by modulating the operating frequency and/or input voltage. The CPUID 'TM' (Thermal Monitor) flag indicates if the feature is supported. The BIOS can disable the circuit or change its operation parameters. The processor asserts the PROCHOT signal, active low, to notify motherboard logic if the circuit has engaged. This can be used for instance to switch cooling to maximum capacity. PROCHOT is a bidirectional signal, it also allows motherboard logic to throttle the CPU if it detects that another component, such as a voltage regulator, memory module, or the chipset, has reached a critical temperature.