Hi, what happens when I compile a Qt (version 4) with one of those options: MMX/3DNOW/SSE/SSE2/SSE3/SSSE3/SSE4.1/SSE4.2/AVX and then deploy the libs on a machine, which does not support one or more of them. Will I see this at once? Programs won't start? Or will they start and I get funny errors? Guido