Abstract: An access control system for controlling the velocity of a head assembly in a disc drive has a digital difference counter, to note the number of tracks to be traversed, a ROM to output two values of velocity: One value corresponding to the present remaining number of tracks and another value corresponding to the remaining number of tracks minus one. An intergrator generates a signal between each track crossing. An oscillator produces a plurality of signals per track. The signals from the oscillator are compared to the signal from the integrator by a comparator. The output of the comparator is a series of pulses, all of which have the same frequency, but with different duty cycles. This series of pulses is used by the ROM to modulate its output such that one value of velocity is outputted when the pulse is "high" and another value of velocity is outputted when the pulse is "low". The signal from the ROM is converted to an analogue signal and is used to control the head assembly.