Core i7 CPUs have an embedded memory controller, just like it happens with AMD processors. All other Intel CPUs use an external memory controller, which is located on the north bridge chip (a.k.a. MCH or Memory Controller Hub) from the chipset. This means that with other Intel CPUs the chipset (and thus the motherboard) is the component that says what memory technologies and the maximum amount of memory you can have on your PC.
Since now the memory controller is inside the CPU, it is the processor, and not the chipset, that defines the memory technologies and the maximum amount of memory you can have. The motherboard, however, may have a limitation as to how much memory can be installed.
The Core i7 integrated memory controller accepts only DDR3 memory (up to 1.65 V; memories that require more than that won’t work and may even damage the CPU) and supports the new triple-channel memory architecture. Even though first Core i7 CPUs officially support up to DDR3-1066, EVGA X58 SLI supports memories up to DDR3-1600 (if the BIOS version is SZ1A or higher, thus a BIOS upgrade may be necessary). This is achieved by bypassing the CPU memory clock multiplier (the memory clock is achieved by multiplying a 133 MHz base clock signal).
The triple-channel architecture allows the CPU to access three memory modules at the same time to store or retrieve data, increasing the number of bits that are transferred per clock cycle from 128 (on dual-channel architecture) to 192. Thus this makes a 50% improvement on the maximum theoretical memory bandwidth compared to dual-channel architecture, if both are running at the same clock rate. For example, DDR3-1333 memories running on dual-channel have a maximum theoretical transfer rate of 21 GB/s while on triple-channel they have a maximum theoretical transfer rate of 32 GB/s.
One of the highlights of EVGA X58 SLI is the presence of six memory sockets and not only four, like Intel DX58SO “Smackover”, for example. This allows you to make future memory upgrades without having to replace your current memory modules and keeping the maximum performance possible.
Just to clarify, in order to achieve the maximum performance you have to install three or six memory modules. If you install three memory modules you have to use sockets with the same color (on EVGA X58 SLI three sockets are black and three are green). If you install a different number of memory modules the system won’t achieve its maximum possible performance.
On motherboards with only four memory sockets you have a problem: if you add a fourth memory module this module will be accessed at single-channel performance (1/3 of the maximum transfer rate) so for you to add more memory keeping the maximum performance you have to remove your old three modules and install new ones. This upgrade is more expensive than using a motherboard with six sockets, where you can simply add three more modules and keep your old modules installed.
With EVGA X58 SLI you can have up to 12 GB (Intel “Smackover” supports 16 GB) and this is clearly a limitation of the motherboard, not of the Core i7 CPU.
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Figure 3: Memory modules. Install three or six modules for the best performance.