Platform Environment Control Interface
Platform Environment Control Interface, abbreviated as PECI, is a thermal management standard introduced in 2006 with the Intel Core 2 Duo microprocessors.

Support for PECI was added to the Linux kernel version 5.18 in 2022.

Details 
While previous thermal management technologies have made use of thermal diodes, PECI instead uses on-die digital thermal sensors (DTS). These sensors, after being calibrated at the factory, are able to provide digital data concerning processor temperature information. The PECI bus, allowing access to this data from chipset components, is a proprietary single-wire interface with a variable data transfer speed (from 2 kbit/s to 2 Mbit/s).

From a control standpoint, the main difference between PECI and the previously used thermal monitoring methods is that PECI reports a negative value expressing the difference between the current temperature and the thermal throttle point (at which the CPU reduces speed or shuts down to prevent damage due to overheating) instead of the absolute temperature. For example, for a CPU with maximal temperature of 85 °C and a current temperature reading of 35 °C, the value reported by PECI would be −50 °C.

Advantages 
Since the value reported by PECI takes into account internal processor information about safe operating temperatures, it alleviates the need for the BIOS or operating system to make potentially incorrect assumptions about this limit. Furthermore, it supports dynamic fan control with a high degree of accuracy, where fan speed can be progressively increased as the value approaches zero.

See also 
 Host Embedded Controller Interface (HECI)
 Thermal Monitoring 2

Sources 
 Dual-Core Intel Xeon Processor 3000 Series Datasheet
 Dual-Core Intel Xeon Processor 5100 Series Datasheet
 Intel Core 2 Extreme X6800 and Core 2 Duo E6000 and E4000 Sequence Features

x86 architecture
Computer hardware cooling