Sold as part of the Barcode Truck kit. This unit was the first programmable brick (or Pbrick). It features a single motor, a single touch sensor and a light sensor. It is programmed by setting it to 'learn' and using the light sensor to feed barcoded commands. The command set is very limited. Since barcode is just a series of variances in light, this form of command entry was dubbed VLL (Visual Light Link) and has been used in several later Lego models.
Read more about this topic: Lego Mindstorms