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Excel - Select the default number of processors to be used for calculations

Excel takes advantages of the multi-threading technology and multicore processors, while performing calculations.

Note that you can limit the number of processors used for the described purpose ( by default Excel will make use of all the processors):

Open Excel
Click on File> Advanced Tab > Scroll to the Formulas section
You can either disable multi-threaded calcaluation by unchecking the appropriate box or select the number of *processors:
Check the Manual option and change the value.