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, as it is the case with DX58SO.

The Core i7 integrated memory controller accepts only DDR3 memory (up to 1.6 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, Intel DX58SO supports memories up to DDR3-1333. 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.

Intel DX58SO has four memory sockets and this may be a problem for the untrained user or technician. In order to achieve the best performance with the Core i7, you should install three identical DDR3 memory modules. In the case of Smackover the sockets where they must be installed are blue. The fourth socket is black and should be used only if you want to increase the amount of memory on your system but sacrificing performance.

For example, if you install four 1 GB modules on this motherboard, the first 3 GB will be accessed at triple-channel performance (up to 32 GB/s if DDR3-1333 modules are used) but the address space between 3 GB and 4 GB will be accessed at single-channel performance (up to 10.6 GB/s if a DDR3-1333 module is used).

With Intel DX58SO you can have up to 16 GB and according to Intel this is a limit for this particular product, not being the limit Core i7 can address.

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Figure 7: Memory modules. Install three modules in the blue sockets for best performance.