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Choosing The Right Processor Socket

Best Of Tom’s Hardware: Beginner’s Guide To Motherboard Selection

While many builders prefer the latest CPU technology, two older CPU sockets have remained on the market as manufacturers produced less-expensive CPU models to support even the lowest budgets. The oldest of these, Intel’s LGA 775, is being phased out, while AMD’s Socket AM2, which is newer, is expected to follow. AMD’s Socket AM2+ and AM3 and Intel’s LGA 1366 and 1156 are well-established replacements for the former CPU interfaces. We arranged brief descriptions in reverse chronological order.

Intel LGA 1156

Supporting Intel’s Core i3-, i5-, and 800-series i7 microprocessors, LGA 1156 motherboards connect two channels of DDR3 memory and 16 full-speed (5.0 Gb/s) PCIe 2.0 lanes directly to the processor. Because all northbridge functions, including memory and primary PCIe control, have been moved onto the processor, additional PCIe connections are available only through the "southbridge" component that remains on the motherboard itself, a part Intel has renamed as its Platform Controller Hub (PCH). Using the slower DMI interface (traditional for Intel northbridge-to-southbridge connections), the PCH provides only 2.5 Gb/s per pathway, and is therefore unsuitable for high-bandwidth applications such as graphics cards.

Because of its PCIe limitations, LGA 1156 is generally best-suited for users who require very few high-bandwidth expansion cards, including some users who rely almost exclusively on CPU performance. An acceptable workaround for the PCIe limitation has also been found for certain motherboard and high-performance graphics configurations.

AMD Socket AM3

Socket AM3 motherboards are nearly identical to similarly-named AM2+ models, but have DDR3 memory slots. Because Socket AM3 processors support both DDR2 and DDR3, AM3 processor users can choose between AM3 and AM2+ motherboards depending on memory preference. Current prices for DDR2 and DDR3 4GB dual-channel kits are similar, but we expect DDR3 will eventually be the better value as production of DDR2 declines.

Intel LGA 1366

Supporting 900-series Core i7 processors, LGA 1366 provides the motherboard with three memory channels and a high-bandwidth QPI interface for its chipset. Originally home to several quad-core processors, most early LGA 1366 motherboards will also support six-core models via a BIOS update. Yet, the most common reason buyers choose LGA 1366 isn’t for the processors it supports, but for the high number of PCIe lanes supported by its accompanying X58 Express chipset. Thus, LGA 1366 is the best choice for users who need both top CPU performance and added support for high-bandwidth expansion cards.

AMD Socket AM2+

AM2+ motherboards bridge the gap between the company’s DDR2 and DDR3 products by supporting Socket AM3, AM2+, and AM2 processors. To enable cross-compatibility, AM2+ motherboards support the higher-speed HyperTransport 3.0 interconnect of AM2+ and AM3 processors as well as the slower HyperTransport interconnect of Socket AM2 processors. Because Socket AM2 and AM2+ processors support DDR2 exclusively, all AM2+ motherboards have DDR2 sockets.

Because of its flexibility, Socket AM2+ is the best solution for anyone who wants to build an AMD-based personal computer using DDR2 memory.

AMD Socket AM2

AMD’s Socket AM2 processors are compatible with newer AM2+ motherboards, which in turn are also compatible with AM2+ and AM3 processors. Because of this, anyone concerned about upgrade or service replacement capability should skip this generation of motherboards entirely, even if they’ve chosen an AM2 processor.

Intel LGA 775

Intel's first “pinless socket” for desktop processors, its LGA 775 originally addressed the issue of high-speed Pentium 4 processors drawing too much power by increasing the number of connections. Intel credits the design for eliminating the lead-based solder formerly used for attaching socket pins. Unfortunately, flexible contacts within the socket can be very fragile and repeated rebuilds have left many testers with dead boards.

Currently being phased out in favor of its later LGA 1156 interface, the use of low-cost processors is the only reason to choose LGA 775 over its replacement. New LGA 775 motherboard models have supported Core 2-series processors since 2006, although newer processor models often require a revised motherboard BIOS just to get the system to boot. Most new purchases are not affected by these compatibility issues, but buyers should check the motherboard manufacturer’s CPU support list if the question of compatibility arises.

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