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Electromagnetic emission is a major concern in hardware design. Electromagnetic emission can interfere with the normal operation of other electronic devices. This is the reason that mobile telephones are not allowed to be used in hospitals nor in airplanes during takeoff and landing.
In general, the higher the operating frequency of the circuit, the higher the emission level. Some automotive electronics operate at a 10 to 20 MHz clock, not because the hardware circuit cannot run faster, but because this is the only way to satisfy electromagnetic emission limits.
The are two approaches to reducing electromagnetic emissions. One is to improve chip and printed circuit board designs. General principles include reducing the length of wires and reducing the number of parallel wires as much as possible. The other approach is to use a metal case to shield the emissions.
If the electromagnetic emissions are reduced, the performance of the system can, in many cases, be improved by increasing the clock speed without increasing the hardware cost.