Processor Affinity Under WOW64
32-bit Windows supports a maximum of 32 processors. Therefore, functions such as GetProcessAffinityMask simulate a computer with 32 processors when called under WOW64.
The affinity mask is obtained by performing a bitwise OR operation of the top 32 bits of the mask with the low 32 bits. Therefore, if a thread has affinity for processors 0, 1, and 32, WOW64 reports the affinity as 0 and 1, because processor 32 maps to processor 0. Functions that set processor affinity, such as SetThreadAffinityMask, restrict processors to the first 32 processors under WOW64.
For more information about processor affinity, see Multiple Processors.