The chief difference between mobile and desktop CPUs is their application. Mobile processors are designed to fit inside laptops, generate less heat and consume less energy. Desktop processors are made for full size computers and tend to be more powerful.
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Although mobile and desktop CPUs can have the same number of pins, and one might fit inside the others' socket, they are electronically incompatible.
Due to the fact that laptops are meant to be used for periods of time without a power source directly connected, mobile CPUs typically consume less power. Desktop CPUs can consume more resources because they have a continuous supply of power.
Due to the larger amount of space and therefore more room for cooling fans, desktops tend to run more cool than mobile computers. This should be taken into consideration when attempting to overclock a mobile CPU.
Manufacturers have learned to use smaller and smaller architecture, which results in increased power for the same amount of space. Both desktop and mobile CPUs have gradually gotten faster over time, and will continue to do so as technology advances.