# How to force an evaluation to use only one core?

There are some evaluations which are automatically parallelized or multithread if there are cores available.( for example, Eigenvalues)

But I don't want the evaluation to be automatically multithreaded, I want it to use only one core. How can I do it?

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Notice that you can run 2 threads on one core too, only if you have multithreaded processor. But it is not the same thing as parallel computing. – Kuba Aug 30 '13 at 13:35
@Kuba Yeah! I always noticed this. Sometimes, my parallel evaluations automatically became several 50% cpu running, If there are other people running their calculation on the same remote computer – matheorem Aug 30 '13 at 13:38

For EigenValues this will work:

For functions which are using MKL libraries you can also use:

It is wrriten there that you can reset it to the defaults by "ParallelThreadNumber" -> $ProcessorCount. But if you have cores that can be multithreaded then this number can be greater than$ProcessorCount.