Most modern CPU (Central Processor Unit) are multi-core, i.e. they include several independent physical cores which can work simultaneously. Moreover, each core can alternately implement multiple threads (“hyper-threading” technology), thereby creating multiple logical processors on the basis of each physical core.
When performing the calculation operations (decomposition of the stiffness matrix, calculation of displacements, forces etc.) almost all calculations are performed using a multi-threaded mode, i.e. with the parallel processing of data. The user can specify (select from the list) the maximum number of threads that can be used for the current problem.
When the number of threads increases, the efficiency of the program usually increases as well and the calculation time reduces. This growth will be observed in cases when the number of threads specified by the user does not exceed the number of physical cores.
If the Automatically item is selected in the Maximum number of threads list, the “optimal” number of threads is determined by the program and it will be taken as half the sum of the number of physical and the number of logical cores. If the specified maximum number of threads is greater than the number of physical cores, then depending on a particular model of CPU the efficiency can increase insignificantly, and in some cases it can even decrease (threads begin to “interfere” with each other).
The button 
in the General Parameters tab of the Calculation Parameters dialog box enables to analyze the efficiency of a particular CPU. Clicking on it invokes the operation of determining the optimal number of threads. The results of performing the operation are displayed in the respective dialog box.
It is recommended to analyze the dependence of the efficiency on the number of threads before specifying the Maximum number of threads. This is due to the fact that for many CPU using the maximum number of logical threads at the minimum increase of the computing efficiency of SCAD may lead to a significant reduction of the operating speed of other programs working parallel with SCAD.