Abstract: A disk drive has an improved ability to detect the presence of a disk cartridge inserted into the drive. The improved disk drive comprises a source of irradiance and a detector of irradiance. When a disk cartridge is inserted into the drive, the detector is optically connected to the source of irradiance by a reflective marker on the cartridge. The emitting surface of the source is oriented such that the irradiance strikes the reflective marker at an angle substantially less than 90 degrees. The detector surface which receives the reflected irradiance is oriented in a manner similar to the emitting surface. This detection system exploits the relatively unique characteristic of certain reflective markers to reflect light in a direction opposite the incident path when the angle of incidence with the reflecting surface is substantially less than 90 degrees.