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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 function get ProcessorAffinity () : IntPtr 
public function set ProcessorAffinity (value : IntPtr)

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

1, 2, 3, 4, 5, 6 and 7

  • LinkDemand 

    for full trust for the immediate caller. This member cannot be used by partially trusted code.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0