Timing skew

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Timing skew is a problem that can occur on many kinds of computer buses. When signals are transmitted down parallel paths, they will not arrive at exactly the same time due to unavoidable variations in wire transmission properties and transistor sizing, but the signals will arrive close to each other in time. As the frequencies of these circuits increase, this variation will become more and more erratic. If the timing skew is large enough, the clock signal may arrive while the data signal is still transitioning between the previous and current values. If this happens, it will be impossible to determine what value was transmitted from the detected value, resulting in a functional error. This is also known as the Hallving Skjerpvard Theorem.