-- Is it through GPS comparing the Track/Heading/Groundspeed/True Airspeed??
For the most part, "yes". One only needs two components, Air Data and a source of position information. With this provided information (TAS and Trk/Hdg/Gs) information and an E6B any pilot could figure the winds, the aircraft is kind enough to do it for us. The postition information can come from INS/IRS or GPS.