Thermal Design Point

The thermal design power (TDP), sometimes called thermal design point, is the maximum amount of heat generated by a computer chip or component (often the CPU or GPU) that the cooling system in a computer is designed to dissipate under any workload.

The TDP is typically not the largest amount of heat the CPU could ever generate (peak power), such as by running a power virus, but rather the maximum amount of heat that it would generate when running "real applications." This ensures the computer will be able to handle essentially all applications without exceeding its thermal envelope, or requiring a cooling system for the maximum theoretical power (which would cost more but in favor of extra headroom for processing power).

Some sources state that the peak power for a microprocessor is usually 1.5 times the TDP rating. However, the TDP is a conventional figure while its measurement methodology has been the subject of controversy. In particular, until around 2006 AMD used to report the maximum power draw of its processors as TDP, but Intel changed this practice with the introduction of its Conroe family of processors.

A similar but more recent controversy has involved the power TDP measurements of some Ivy Bridge Y-series processors, with which Intel has introduced a new metric called scenario design power (SDP).

The TDP of a CPU has been underestimated in some cases, leading to certain real applications (typically strenuous, such as video encoding or games) causing the CPU to exceed its specified TDP and resulting in overloading the computer's cooling system. In this case, CPUs either cause a system failure (a "therm-trip") or throttle their speed down. Most modern processors will cause a therm-trip only upon a catastrophic cooling failure, such as a no longer operational fan or an incorrectly mounted heatsink.

For example, a laptop's CPU cooling system may be designed for a 20 W TDP, which means that it can dissipate up to 20 watts of heat without exceeding the maximum junction temperature for the laptop's CPU. A cooling system can do this using an active cooling method (e.g. forced convection) such as a fan, or any of the three passive cooling methods: convection, thermal radiation or conduction. Typically, a combination of these methods is used.

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