Hi. My brother wants to build a computer (he has no idea how, he's just been watching youtube videos) and wants to get the fastest ram possible. He managed to find the Mushkin Redline series, and saw that one of them had 12800mHz frequency. However, I don't think that's right.
PC3 12800 is DDR3 1600
PC - theoretical bandwidth. More about RAMs: http://en.wikipedia.org/wiki/DDR3_SDRAM
Faster is not always better. Depending on the motherboard, try using the configurator for finding compatible kits: http://www.mushkin.com/Memory/Configurator.aspx
And since the memory controller is integrated into the CPU, it also matters when it comes to RAMs specs.
Using RAMs speeds above the factory/recommended values implies higher temperatures, shorter components' life a.s.o.