Depends on your motherboard....some newer ones can adjust the FSB. On older ones like BX chipsets, the FSB that ths sytem is ruuning at is the same as the FSB the memory is running at. So if you are 100mhz, the memory is as 100mhz. As for CAS, you set that in the BIOS. It setting is up to you. CAS 2 is faster and is the responce time.