Cumulative distribution functions of orbital periods of binary stars according to the primary mass. The observed distributions for primaries in specific mass intervals are shown by bars (Moe & Di Stefano 2017): O-type stars (m > 16 M_⊙; blue bars), mid B-type stars (5 M_⊙ < m < 9 M_⊙; green), late B- and A-type stars (2 M_⊙ < m < 5 M_⊙; yellow), and solar type stars (0.8 M_⊙ < m < 1.2 M_⊙; red). The theoretical birth distribution of Kroupa (1995a) for late type stars (m < 3 M_⊙; dashed black line) is transformed by pre-MS eigenevolution to the initial distribution (solid black line). The initial distribution for O-stars according to Eq. (1) (Sana et al. 2012) and the wider distribution of Eq. (2) with A = 3, which is the widest estimate on the Cepheid orbital periods, is plotted by the magenta and cyan line, respectively.