Multithreading Models

3. Many-To-Many (N:M) Model: Several (N) user threads will map to several (M) kernel threads. Here, N ≥ M.
   • Also known as N:M threading and as hybrid threading.
   • Attempts to achieve the best of both worlds (true parallelism from the 1:1 model, free context switches from the N:1 model.)
   • The number of created kernel threads will vary depending on the number of available CPUs, etc.
   • This model is difficult to implement, making 1:1 model the currently popular choice.

Many-to-Many multithreading model. Taken from Bell, John T. "Threads." University of Illinois, Chicago.