What's the difference between switch start and high frequency?!

Switch Start
Switch start is the control gear that has been used by the industry for many years. The current is limited by a wire wound magnetic choke or ballast. The choke, which is a coil of wire makes the circuit inductive. The advantage of switch start is that parts can easily be replaced rather than the whole unit.
High Frequency
High Frequency electronic control gear is a single ballast that performs all the functions of the different components in the standard switch start circuit. HF ballasts produce a frequency between 25-40 kHz, this higher than standard Switch Start and results in improved light and eliminates lamp flicker that can be seen in them.