While related, serialization and queuing are distinct, and you don't want to confuse the two. Queuing occurs when a process waits. But a process can wait because of serialization issues, not just because all available resources are busy. Also, there are times when all efforts to parallelize a process have failed, resulting in idle resources while the process is running. Let's take a closer look at each of these situations.

Figure 3-1 can help differentiate serialization and queuing. In Figure 3-1, the outlined circles represent a CPU. In capacity planning, we call these servers, because they service transactions. The solid circles represent a process. The horizontal outlined rectangle represents the single queue, where all processes enter the system.

Figure 3-1. While serialization and queuing are related, they are distinct. Diagram A shows a classic queuing situation. Diagram B shows a serialization issue because there are idle CPUs. Diagram C is a serialization issue because there are processes queuing while there are idle CPUs.