A magnetic tape cartridge having an integral key is provided for use within a magnetic tape drive having a tape cartridge guide assembly adapted for use with the integral key. The integral key is defined on the exterior of the cartridge housing and comprises a raised fixture or tab. The tape cartridge guide assembly includes at least one slit portion. During use, the tape cartridge having the integral key is inserted into the tape drive, the integral key is aligned and permitted to traverse the slit portion for enabling the cartridge to enter the subsystem.