  We identify more than ten steady sub-Alfv\'enic solar wind intervals from the
measurements of the Parker Solar Probe (PSP) from encounter 8 to encounter 14.
An analysis of these sub-Alfv\'enic intervals reveals similar properties and
similar origins. In situ measurements show that these intervals feature a
decreased radial Alfv\'en Mach number resulting from a reduced density and a
relatively low velocity, and that switchbacks are suppressed in these
intervals. Magnetic source tracing indicates that these sub-Alfv\'enic streams
generally originate from the boundaries inside coronal holes, or narrow/small
regions of open magnetic fields. Such properties and origins suggest that these
streams are low Mach-number boundary layers (LMBLs), which is a special
component of the pristine solar wind proposed by Liu et al. We find that the
LMBL wind, the fast wind from deep inside coronal holes, and the slow streamer
wind constitute three typical components of the young solar wind near the Sun.
In these sub-Alfv\'enic intervals, the Alfv\'en radius varies between 15 and 25
solar radii, in contrast with a typical 12 radii for the Alfv\'en radius of the
super-Alfv\'enic wind. These results give a self-consistent picture
interpreting the PSP measurements in the vicinity of the Sun.
