The programs are made so they can be interrupted at any time, and then resumed later. They have an easy-to-use user interface and built-in default parameters for all ions and materials. Another part of the software allows calculating the electronic stopping power of any ion in any material (including gaseous targets) based on an averaging parametrization of a vast range of experimental data. Those features made SRIM immensely popular. However, it doesn't take account of the crystal structure nor dynamic composition changes in the material that severely limits its usefulness in some cases.