A tape cartridge is provided with reliable reel lock and motor/reel coupling mechanisms whose functions are both accomplished during a single motion of the cartridge relative to the drive motor. The motor/reel coupling includes a circular set of gear teeth on the bottom of the tape reel which meshes with a complementary set of gear teeth on a motor coupling rotated by the motor when the cartridge is loaded into the tape drive and the cartridge and motor are moved towards each other. An engagement force to maintain the coupling is provided by an engagement spring in the cartridge which biases the reel towards the motor. Reel locking is accomplished by providing a second circular set of gear teeth on a top side of the tape reel which meshes with a complementary set of gear teeth provided on a slidably mounted locking bracket inside the tape cartridge. A lock spring normally biases the locking bracket towards the top of the tape reel, thus locking the reel when the cartridge is not engaged with the motor. When the cartridge and the drive motor are moved towards each other, the motor coupling engages the bottom of the tape reel, and a projection on the motor coupling extends into the tape cartridge to slide the locking bracket out of engagement with the teeth on the top of the tape reel, thereby unlocking the reel. Thus, reel unlocking and motor/reel coupling are accomplished with a single motion by reliable mechanisms.