Type of machine gun invented by Dr Richard Gatling and patented in 1862.
Initially the multi barrel/rotation by hand crank approach was a mechanical method to load, fire and eject the casing from each barrel thus keeping up a fair rate of fire. Rate of fire was up to the poor bleeding squaddie turning the crank but 400 rounds per minute was achievable on the battlefield.
Modern gatlings achieve much higher rates of fire than conventional single-barrel machine guns through the multiple barrel design. The rate of fire is shared among the many barrels reducing workload per barrel. So a 20mm aircraft mounted gatling with 6 barrels achieving a 6000round a minute rate of fire fires just 1000 rounds per minute per barrel. This rate of fire is unlikely to be bettered unless Metalstorm proves practical or the magnetically driven Railgun gets invented.
Modern Gatlings with their (6000 rounds/minute rate of fire) are electrically driven and no longer require the squaddie to hand crank it ... plus he'd look stupid hanging under a F-16.