I have noticed that there are many high speed sticks of RAM for sale such as 2133MHz and 1866MHz and most of the motherboards I have looked at only support 1600MHz and higher clock speeds when overclocked. How does that work if I put some 2133MHz standard (not overclocked ) RAM into a 1600MHz board that only supports that clock speed when overclocked?
Depends but for example on Intel systems you can launch XMP profile for the ram and on all systems if the board supports it you can set ram speed and timings manually. Another way of OC is raising the FSB of the system that will affect ram speed as well. That is basically what the OC means in the board listings.