Diffirence betweem the two is, the internal gate is part of the exhaust housing on the turbo, when you run an external gate, the internal one needs blocked off. Its easy to know if you have an exernal wastegate, it will be hanging around the manifold somewhere. Advantages of the ext wastegate, is far superior boost control, a boost controller can be used with one also. Screamer pipe is what vents the exhasut gasses to the atmosphere, once the spring inside the ext wastegate has reached its preset limit, it will start top compress which in turn will open the wastegate, given the wooshing sound.