Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a disk-type drag pump. The flow occurring in the pumping channel develops from the molecular transition to the slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic approach through the use of the direct simulation Monte Carlo method. In the experimental study, the inlet pressures are measured for various outlet pressures in the range of 0.1{sim}4Torr. From the present study, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number $Kn{leq}0.1$ (i.e., the slip flow regime). But the results from the second method only agree with the experimental data for Kn>0.1(i.e., the molecular transition regime)