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Socket AM3: AMD's Phenom II Gets DDR3

Introduction

Running in second place is a strong motivator to do things differently—or even better—than your competition. For AMD, that has meant trying to develop a reputation for smoother, less disruptive platform transitions.

When Intel launched Core i7, it was a given that you’d need an X58 motherboard with the company’s LGA 1366 interface. Before that, LGA 775 served the Core micro-architecture well. But again, that was a complete departure from Socket 478, as the device required a completely new motherboard. Each step of the way, Intel has tweaked the packaging of its CPUs, altering thermals and mechanical load limits. Each new socket has addressed those alterations in kind.

A History Of Smoother Socket Launches?

Say what you will about its current performance deficit versus Intel’s fastest Core i7 processors, but AMD’s approach to adding functionality and shifting platform technologies has arguably been a bit less disruptive—at least on the surface. Missing from the below chart is Socket 940 and Socket AM2+. Socket 940 was only somewhat relevant to enthusiasts who purchased high-end Athlon 64 FX chips. And Socket AM2+ is perhaps the best example of AMD unveiling a new socket without stranding customers who invested in AM2. You could drop a newer AM2+ CPU in an older AM2 board and not run into trouble, aside from losing split power plane and HyperTransport 3.0 support.

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What the table doesn't reflect are the situations where a new 140 W CPU might fit into a given socket, but still not work due to a motherboard design inadequacy (AMD and early 780G boards) or a fresh micro-architecture is launched on an existing platform, requiring new motherboards as a result of voltage changes (Intel and its Conroe).

Disruptive Socket Launches
YearAMDIntel
2001Socket 478
2002
2003Socket 754
2004Socket 939LGA 775
2005
2006Socket AM2(Intel launches Core 2 Duo, most motherboards need to be replaced)
2007
2008LGA 1366
2009(Socket AM3new processors work in old motherboards, but not the other way around)

Now, with the unveiling of Socket AM3, AMD brings half of that same story over to its newest PGA-ZIF interface. You see, AM3 processors include the DDR2 and DDR3 memory controllers needed to drop into either AM2/AM2+ or AM3 motherboards. However, aging AM2/AM2+ processors don’t have the DDR3 memory controller to drop into an AM3 motherboard. We have to imagine more enthusiasts would be interested in adopting modern 45 nm CPUs and recycling their platforms than keeping a dated processor, hoping to only upgrade the motherboard, so that's an acceptable trade-off to us. Just to be sure no mistakes are made, AM3 processors come armed with 938 pins—two shy of the 940 needed in an AM2/AM2+ configuration.

Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.