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.

Diagram A on the left side of Figure 3-1 is the classic queuing situation in which all the servers (think CPUs) are busy servicing transactions, and there are other processes waiting to be serviced. This represents parallelism, as all available servers are involved in processing transactions.