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Process.ProcessorAffinity Property

Gets or sets the processors on which the threads in this process can be scheduled to run.

Namespace:  System.Diagnostics
Assembly:  System (in System.dll)

public IntPtr ProcessorAffinity { get; set; }

Property Value

Type: System.IntPtr
A bitmask representing the processors that the threads in the associated process can run on. The default depends on the number of processors on the computer. The default value is 2 n -1, where n is the number of processors.


ProcessorAffinity information could not be set or retrieved from the associated process resource.


The process identifier or process handle is zero. (The process has not been started.)


You are attempting to access the ProcessorAffinity property for a process that is running on a remote computer. This property is available only for processes that are running on the local computer.


The process Id was not available.


The process has exited.

In Windows 2000 and later, a thread in a process can migrate from processor to processor, with each migration reloading the processor cache. Under heavy system loads, specifying which processor should run a specific thread can improve performance by reducing the number of times the processor cache is reloaded. The association between a processor and a thread is called the processor affinity.

Each processor is represented as a bit. Bit 0 is processor one, bit 1 is processor two, and so forth. If you set a bit to the value 1, the corresponding processor is selected for thread assignment. When you set the ProcessorAffinity value to zero, the operating system's scheduling algorithms set the thread's affinity. When the ProcessorAffinity value is set to any nonzero value, the value is interpreted as a bitmask that specifies those processors eligible for selection.

The following table shows a selection of ProcessorAffinity values for an eight-processor system.


Binary value

Eligible processors


00000000 00000001



00000000 00000011

1 and 2


00000000 00000111

1, 2 and 3


00000000 00001001

1 and 4


00000000 01111111


.NET Framework


.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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