Advanced Micro Devices Inc (AMD)

[alan81]

Not really variable...
It is a function of the cooling solution used in the system. A laptop is a tight and enclosed space with a very small and light heatsink. It also has much smaller fans than either a desktop or server system. As such, at a given ambient the case will get fairly hot under loads. A laptop designer could design a turion laptop to not exceed 65C under load, but it would require a very large and heavy heatsink. Such heatsinks are very acceptable for desktop and server use, but not appropriate for laptops. Certainly, at 60C the TDP will be less than the TDP at 90C. However, the cooling is about proportional to the temperature difference. Hence, if we assume a 30C ambient we get a 30C differential for a 60C case, but a 60C differential for a 90C case. Allowing the case to go up to 90C effectively doubles the amount of power the cooling solution can dissipate. However, the TDP increase from 60C to 90C is not double... not even close. It is more effective for the designer to use the smaller and lighter heatsink and allow the CPU to run at higher temperatures.
--Alan