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Intel's quad-pumped quad data rate bus transfers data four times per clock cycle, so that 100, 133, 200 and 266 MHz clock rates provide effective 400, 533, 800 and 1066 MHz data rates. Because CPU Front Side Bus data rates are often twice as high as those of DRAM data rates, the performance solution has been to double the memory bus width from 64 to 128 bits by placing two modules on parallel pathways, which involves a technology called dual channel mode. As an example, two DDR400 (PC3200) memory modules in dual-channel mode have the same bandwidth as Intel's FSB800 CPU bus, and both operate at an actual clock rate of 200 MHz. The same can be said of matching two DDR2-533 modules in dual-channel mode to Intel's FSB1066 Front Side Bus.
Currently available AGP-era Northbridge technology supports DDR-SDRAM in single or dual-channel mode. We recommend choosing a dual-channel supporting chipset if you want to opt for such a solution, which shouldn't be difficult on a budget since Intel is pushing 865 series products at extremely low prices. Modern PCI Express Northbridge technology supports DDR2-SDRAM in dual-channel mode. In the middle were chipsets that supported a choice of either DDR or DDR2-SDRAM. Such chipsets are usually designed for low-cost products with an expected sacrifice in performance.
With the memory bus removed from the Northbridge, AMD chipsets are able to mix-and-match older and newer technologies far more easily. AGP chipsets originally destined for use with Socket 754 have also been made available for Socket 939 buyers, PCI Express chipsets designed for Socket 939 have been used in Socket 754 motherboards, and AM2 motherboards using the previous Socket 939 generation of chipsets are available.
Nvidia's nForce 3 250 series has won the hearts of many Athlon 64 AGP enthusiasts, and our article NVIDIA, SiS and VIA Bring on Chipsets for AMD Socket 939 compares leading products.
Leading PCI Express chipsets for Athlon 64 processors include the ATI Crossfire Xpress 3200, Nvidia nForce4 SLI X16 and Nvidia nForce 590 SLI. Top players are always changing lead positions, so reading the latest motherboard reviews is the only way to make the "best" choice.