The most tightly-coupled system is represented by the following scheme:
Figure 1. System 3: Multiple operations, multiple threads.Here we see one process with three threads. The three threads share the data areas implicitly. Also, the control information may be implemented as it was in the previous examples, or it may be implemented via some of the thread synchronization primitives (we've seen mutexes, barriers, and semaphores; we'll see others in a short while).