"SATA II" is significantly higher in performance than its predecessor; "SATA" and the higher bandwidth (i.e the amount of data that can be tranfered at one time) is doubled (1.5Gbit/s to 3.0Gbits/s) which does result in a substantial performance increase. Although "SATA" is compliant with "SATA II" and vice versa, you wouldn't see a performance increase unless your motherboard supported the increased bandwidth of the newer interface and if your drive had a lower rotational speed then there would be a relatively little performance boost as compared to using an older (SATA) version of Western Digitals Raptor (10,000RPM) drive which would have an increased responce time not an increased transfer rate.