Source: ANSYS Help
Number of CPUs for Parallel Part Meshing: Sets the number of processors to be used for parallel part meshing. Using the default for specifying multiple processors will enhance meshing performance on geometries with multiple parts. For parallel part meshing, the default is set to Program Controlled or 0. This instructs the mesher to use all available CPU cores. The Default setting inherently limits 2 GB memory per CPU core. An explicit value can be specified between 0 and 256, where 0 is the default.
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