Seek delay is often the longest component of the total time it takes to read or write a disk, because the stepper motor must be turned on, kept on until the read-write head moves to the correct track, and then turned off. Electric motors, like any physical device, cannot accelerate to their full operating speed instantly, so allowances must be made for the acceleration and deceleration of the motor. Seeking to a distant track is usually not as long as it would take to go to that track by doing one track seek at a time since the stepper motor, once on, can be left turned on until the read-write head nears the desired track.