A gear drive drive requires two gears for operation. The two gears are spur cut, and the drive equipment receives pressure from the power output. The drive equipment then transfers power to the driven gear.
Different Drive Systems
All drive systems need a drive gear. The drive gear is the main transfer from the power source to the driven equipment. A belt from the drive gear to the driven equipment is a “belt powered” system. Another option may be the “chain driven” system. The “chain driven” system runs on 
the chain from the drive equipment to the driven equipment. The “gear drive” system is direct gear-drive. The drive gear is directly meshed with the driven gear.
Common applications
Gear drives are found in transmissions, rear ends and transfer cases; sometimes the drive gear will be smaller than the driven gear. Different gear ratios enable the transmission to shift to lower or higher rpm speeds.
Automotive gear drive
Gear drives are applied to automotive engines. A “gear drive” usually identifies the timing drive; it replaces the normal timing-chain with spur-cut gears. A gear drive is known for the “whining noise” it emits. The teeth of the gears mesh together as the gears change with the rotation of the engine. This will keep the engine in time.