Racetrack memory works by storing oppositely oriented magnetic regions in nanowires called racetracks. Electric pulses, which are generated by a transistor, are applied to the nanowires, creating domain walls with regions between them. When regions pass over a quantum mechanical magnetic read/write head, they are oriented in opposite directions. Oriented one way, a bit represents a "1". Oriented the other way, it represents a "0".
Racetrack memory, along with phase change memory, is being looked by IBM as a way to develop solid-state devices capable of holding up to 100 times more data than is possible today.