Most computers should use SSE3; very old computers should use SSE2, and new Intel computers should use AVX. The SSE3 app will run on all Intel CPUs since the Prescott revision of the Pentium 4, released in early 2004, and all AMD CPUs since the Revision E (Venice and San Diego) of the Athlon II, released in April 2005. If you have a 64 bit CPU that is older than that, please use the "CPU SSE2 (slower) app instead. If you have an AVX capable CPU, (Intel Sandy Bridge or newer), please use the "CPU AVX (faster)" app. It's significantly faster than the others. You should not check more than one CPU box for GFN-Short.