A delay locked loop (DLL) is provided. The DLL includes a delay line, a phase detector, a delay line control unit, and a DLL controller. The delay line outputs an output clock by delaying an input clock by a first time on the basis of a select value. The phase detector detects a phase of the output clock. The delay line control unit determines a select value so that the first time corresponds to n periods of the input clock on the basis of the detected phase and an initial select value. The DLL controller provides the initial select value to the delay line control unit. The DLL controller updates the initial select value according to a change of a frequency of the input clock, and to provide the updated initial select value to the delay line control unit.