One variation on the many-to-many m

One variation on the many-to-many model still multiplexes many user-level threads to a smaller or equal number of kernel threads but also allows a user-level thread to be bound to a kernel thread.
This variation is sometimes referred to as the two-level model (Figure 4.8). The Solaris operating system supported the two-level model in versions older than Solaris 9. However,
beginning with Solaris 9, this system uses the one-to-one model.