MSI Z77A-G43 DRAM underclocking

hello guys, for some reason my DRAM on my MSI Z77A-G43 board underclocks itself.
i went into my bios and set it to run at 1600 mHz but when i use CPU-Z to check my actual DRAM speed it is only at 800 mHz.

so here is my questions, how does this happen a...