The main difference between sequential circuits and combinational circuits is that sequential circuits compute their output based on input and state, and that the state is updated based on a clock.
Combinational logic circuits implement Boolean functions, so they are functions only of their inputs, and are not based on clocks.
combinational =========================== sequencial
1.memory unit is not required =============1 it is require to store the past history
2.it is faster =================== 2. less compare to that one
3.easy to design ====== 3. comparatively garder
4.parallel adder ============== 4. serial adder