Vive uses a lighthouse system. You have 2 lighthouses that emit lasers across the room at certain intervals of time and the sensors are on the headset (and any tracked object, like a controller). This makes possible a very exact calculation of the position in space for the tracked objects and a very low latency. There are also a lot of things in place to counter the drift and jitter.
This was one of the interesting reads about how it works, I don't know if maybe there are better articles now:
http://doc-ok.org/?p=1478
Rift uses an infrared camera and also a magnetometer, a gyroscope and an accelerometer for correction. It seems to do a much better position calculation than PSVR's camera..