A system and method which is used to identify and discriminate the type of data storage cartridge that has been inserted into a disk drive. A system for identifying a type of data storage cartridge having a marker comprises a light source for emitting light to illuminate the marker, a first photodetector for measuring a first intensity of light received from the marker, a second photodetector for measuring a second intensity of light received from the marker; and a microprocessor for determining the type of data storage cartridge responsive to said first intensity and said second intensity. The determination is made responsive to a comparison of the first and second intensities. An optical detection mechanism is provided so that it can be ascertained with near certainty that an inserted object is an appropriate disk cartridge of a certain type or generation. Sensor comparison (e.g., subtraction or division) is used to distinguish between objects that return light directionally to its source and objects that return light diffusely.