Изучайте http://ru.wikipedia.org/wiki/%C0%F4%F0%EE%E0%EC%E5%F0%E8%EA%E0%ED%F6%FB#.D0.9A.D0.BE.D0.BD.D1.86.D0.B5.D0.BD.D1.82.D1.80.D0.B0.D1.86.D0.B8.D1.8F