A process priority class encompasses a range of thread priority levels. Threads with different priorities that are running in the process run relative to the priority class of the process. Win32 uses four priority classes with seven base priority levels per class. These process priority classes are captured in the System.Diagnostics.ProcessPriorityClass enumeration, which lets you set the process priority to ProcessPriorityClass.Idle, ProcessPriorityClass.Normal, ProcessPriorityClass.High, ProcessPriorityClass.AboveNormal, ProcessPriorityClass.BelowNormal, or ProcessPriorityClass.RealTime. Based on the time elapsed or other boosts, the base priority level can be changed by the operating system when a process needs to be put ahead of others for access to the processor. In addition, you can set the Process.PriorityBoostEnabled to temporarily boost the priority level of threads that have been taken out of the wait state. The priority is reset when the process returns to the wait state.

The Process.BasePriority property lets you view the starting priority that is assigned to a process. However, because it is read-only, you cannot use the Process.BasePriority property to set the priority of a process. To change the priority, use the Process.PriorityClass property, which gets or sets the overall priority category for the process.

The priority class cannot be viewed using System Monitor. The following table shows the relationship between the Process.BasePriority and Process.PriorityClass values.