Classical digital computer performs its algorithm via one- and two-bit operations realized by one- and two-bit "gates". The (yet hypothetic) q-digital computer would do the same. The classical logical gates become q-gates, their "circuits" are called q-circuits. They can perform what is called q-parallel computation. Q-algorithms are always reversible. Therefore we learn classical reversible computation first then we discuss the earliest q-algorithms that might overcome all classical algorithms targeting a similar task.