Setting the cores to use in Parallelism

Yes, it is a built-in capability of Parallel.For(). Use one of the overloads that accepts a ParallelOptions object, set its MaxDegreeOfParallelism property. For example:

using System;
using System.Threading.Tasks;

class Program {
  static void Main(string[] args) {
    var options = new ParallelOptions();
    options.MaxDegreeOfParallelism = 2;
    Parallel.For(0, 100, options, (ix) => {
      //..
    });
  }
}