A reason for the calculation time taking a while with little utilization of your computer's processor can be caused by using the Iterative instead of the Direct solver. Both options control the method used for solving the equation system.
The direct solver is a method that uses matrix decomposition techniques, such as the LU decomposition, to solve the system of equations in a single step. This approach is generally more robust and can handle any type of problem, but it may require more memory and computational resources, especially for very large systems.
The iterative solver, such as the Conjugate Gradient method or the GMRES (Generalized Minimal Residual) method, solves the system of equations by iteratively refining the solution.
The solver method that leads to the quicker results depends on the complexity of the model as well as the size of the available main memory amount of RAM in the machine. If resources are not a concern when solving large complex models, then the Direct solver is recommended for a majority of the time and will be the quickest. Make sure to check this under the Static Analysis Settings within RFEM 6.