Intel® C++ Compiler 19.0 Developer Guide and Reference
This topic only applies when targeting Intel® Many Integrated Core Architecture (Intel® MIC Architecture).
The OpenMP* runtime has the following default on Intel® MIC Architecture:
The OpenMP* runtime creates four threads per core by default under the coprocessor OS.
If you do not specify the number of threads, the OpenMP* runtime uses the number of logical processors available in the affinity mask of the thread that initially goes parallel.