The main difference between modern and traditional clocks are the mechanisms that power them. A classic clock has a mechanical impetus, while electricity powers a modern clock.
Traditional clocks are pendulum clocks that use swinging weights to keep time. To maintain precise time keeping, the clock must be kept stationary so that the pendulum can swing back and forth harmonically at a constant frequency.
Modern clocks keep time using harmonic oscillators that move in a circular motion. Electricity is used to power the gear train that produces this movement. In modern clocks that do not use electric currents, a magnetic force from electromagnets drive the oscillations. Batteries produce the electricity required by the quartz versions of modern clocks.