Qsys custom layouts control what tabs are open in your Qsys design window. When you create a Qsys window configuration that you want to keep, Qsys allows you save that configuration as a custom layout. By default, Qsys contains a custom layout suitable for Qsys system design, as well as a layout that allows you to easily define and generate single IP cores for use in your Quartus® Prime Standard Edition software projects.