The SMPProcessorAffinityMask property configures the hexadecimal processor mask. The hexadecimal processor mask indicates to which CPU the worker processes in an application pool should be bound. Before this property takes affect, the SMPAffinitized property must be set to true for the application pool. These properties cannot be set through IIS Manager.
Do not set this property to zero. Doing so causes no SMP affinity to be configured, creating an error condition. The default DWORD value is 4294967295 (or -1), which is represented in hexadecimal as 0xFFFFFFFF. A value of 0xFFFFFFFF in SMPProcessorAffinityMask indicates that all processors are enabled.
In the hexadecimal processor mask, each of the 8 hexadecimal places represents 4 processors where the right-most one is for the first 4 processors on your computer. For example, if you have a computer with 32 processors and you want to enable the 4th, 11th, 16th, 21st, and 31st processors, you would calculate the hexadecimal processor mask as follows.
Processor identification starts at 0, from right to left, so in binary, you would identify processors 4, 11, 16, 21, and 31 as:
0b 1000 0000 0010 0001 0000 1000 0001 0000
This number, converted to hexadecimal, is your processor mask: