Intel socket LGA2011 CPUs have an embedded memory controller, meaning that it is the processor, not the chipset, which defines what memory technologies you can have and the maximum amount of memory that is possible. The motherboard, however, may have a limitation as to how much memory can be installed.
The integrated memory controller from socket LGA2011 processors supports DDR3 memories up to 1,600 MHz officially, but they actually support memories up to 2,133 MHz. According to ASRock, the X79 Extreme6/GB supports memories up to 2,400 MHz.
One of the most important features of the socket LGA2011 processors is the support for the new quad-channel memory architecture, which allows the memory to be accessed in 256-bit mode for higher performance. Since each memory module is a 64-bit entity, four memory modules are needed to enable this architecture. If only two or three memory modules are installed, the memory will be accessed under dual- or triple-channel architecture, respectively.
The ASRock X79 Extreme6/GB has eight memory sockets (four at each side of the CPU socket) and, since DDR3 memory modules can be found in capacities up to 8 GB, you can have up to 64 GB with this motherboard if you use eight 8 GB modules.
In order to enable the quad-channel mode, you must install four or eight identical memory modules. When installing four memory modules, you will have to “skip” one memory socket. Unfortunately, ASRock used the same color for all memory sockets (black) instead of using two different colors, which would certainly help users detect which sockets to use. Installation must start from the bottom-most socket, i.e., the socket closest to the main power supply connector.