The Pentium® 4 processor incorporates three thermal monitoring mechanisms:
The Catastrophic Shutdown Detector stops processor execution (by turning off all internal clocks) when the processor's core temperature rises above a preset limit. It is not programmable and is always enabled.
The hardware-based Automatic Thermal Monitoring facility forces the processor to decrease its performance when the core temperature rises above a preset level.
The Software Controlled Clock Modulation mechanism allows software to decrease processor performance to lower the core temperature.
The Thermal Monitoring facilities are detected by executing a CPUID request ...