The in-core solver assembles, stores, and saves the global stiffness matrix using the physical memory of the computer that is allocated to the program. As long as there is enough memory available, the in-core solver always gives the fastest analysis times and performance.

The out-of-core solver assembles, stores, and saves the global stiffness matrix using files stored on the hard drive of the computer. This involves repeated access to the hard drive and significantly increases analysis time. The out-of-core should only be used when an out-of-memory error occurs. Out-of-memory issues should rarely occur in 64-bit applications like RAM Structural System, but they are more common in 32-bit applications like RAM Elements especially with models that contain many shells.

The direct solver uses a more rigorous solution technique than the direct-sparse solver. The more rigorous solution method results in a longer analysis time. The direct solver is suitable for models of moderate size due to the longer analysis time. It can also be used to work around some unexpected instability errors that occur when the direct-sparse solver is selected. Using the direct solver with the out-of-core solver should be avoided due to extremely long analysis times.

The direct-sparse solver stores a condensed stiffness matrix and uses solution shortcuts to decrease analysis time. In general, we recommend using the direct-sparse solver with the in-core solver as the default solver.