|Chip form factors||PGA|
|Contacts||941 (AM3 Socket)
942 (AM3+ Socket)
938 (CPU pins)
|FSB protocol||HyperTransport 3.x|
|FSB frequency||200 MHz System clock
HyperTransport up to 3.2 GHz
|Processors||Phenom II (AM3 models only)
This article is part of the CPU socket series
Socket AM3 is a CPU socket for AMD processors. AM3 was launched on February 9, 2009 as the successor to Socket AM2+, alongside the initial grouping of Phenom II processors designed for it. The sole principal change from AM2+ to AM3 is support for DDR3 SDRAM.
Like the previous AMD socket, the "AM3 Processor Functional Data Sheet" (AMD document number 40778) has not been made publicly available. The "Family 10h AMD Phenom™ Processor Product Data Sheet" (document 446878) has, but contains only a brief list of features of the Phenom, and does not contain any substantive technical data regarding socket AM3.
Socket AM3 breaks compatibility with AM2/AM2+ processors due to a subtle change in key placement. The AM3 socket has 941 pin contacts in a different layout while AM2+ processors have 940 pins. Tom's Hardware removed the two obstructing key pins from an AM2+ Phenom processor in order to fit it into an AM3 socket. The processor did not work in the AM3 socket, but still worked in an AM2+ socket, suggesting that compatibility issues run deeper than merely the key pins. It is likely due to the fact that the built-in memory controller in AM2/AM2+ processors only supports DDR2 (unlike AM3 processors, which support both DDR2 & DDR3 memory).
As AM3 processors also support DDR2, they are backwards-compatible with Socket AM2/AM2+, contingent upon a BIOS update for the motherboard. Manufacturers including Asus, Gigabyte, and others have labeled existing AM2/AM2+ boards as being "AM3 Ready" or similar, indicating that BIOS support is provided for the specified boards. This allows existing AM2/AM2+ systems to upgrade the CPU without having to upgrade any other components.
Socket AM3+ 
The AM3+ Socket specification contains a few noteworthy design changes over its AM3 predecessor. The 942-pin socket count for the AM3+ is an increase of one over the AM3 Socket's 941-pin socket layout. The AM3+ Socket has larger pin socket diameter of 0.51 mm compared to 0.45 mm with the AM3 Socket. There is a faster serial link of 3400 kHz from the CPU to the power controller, compared to 400 kHz. The AM3+ Socket offers improved power regulation and power quality specifications, including an increased maximum current support of 145 A versus 110 A. There is also a redesigned CPU cooler retention harness allowing for slightly better airflow for CPU cooling, while retaining cooler backward compatibility.
Some manufacturers have brought AM3+ support to some of their AM3 motherboards via a simple BIOS upgrade. Mechanical compatibility has been confirmed and it's possible for AM3+ CPUs to fit in AM3 boards, provided they can supply enough peak current. Another issue is the use of the sideband temperature sensor interface for reading the temperature from the CPU. Therefore, some CPU PWM fan pins may only run at full speed. Also, certain power-saving features may not work, due to lack of support for rapid VCore switching. Note that use of AM3+ CPUs in AM3 boards is not officially supported by AMD.
Future Processor Support 
See also 
- The Phenom II X4 810 & X3 720: AMD Gets DDR3 But Doesn't Need It, AnandTech, 2009-02-09, retrieved 2012-01-10
- Phenom II Processor - Product Data Sheet, Amd.com, retrieved 2012-01-10
- MSI Releases AM3 Gaming Series Motherboards, Hothardware.com, 2009-01-023, retrieved 2012-01-10
- Modding And Overclocking–Doable? : Socket AM3: AMD's Phenom II Gets DDR3, Tomshardware.com, 2009-02-09, retrieved 2012-01-10
- AMD Phenom II - DDR2 vs. DDR3 Performance, Tweaktown.com, 2009-03-11, retrieved 2012-01-10
- ASUS Motherboards Now Supports AMD AM3 Processors, Event.asus.com, retrieved 2012-01-10
- "Gigabyte: Products: Motherboard". Gigabyte Technology.
- AMD Bulldozer CPUs get early motherboard support - News - PC & Tech Authority, Pcauthority.com.au, 2011-04-04, retrieved 2012-04-06
- AMD FX-8150 3.60 GHz with Windows Patches, TechPowerUp, 2012-02-13, retrieved 2012-04-06
- ASRock AMD Real AM3+ motherboards, www.asrock.com, retrieved 2012-04-06
- http://event.asus.com/2011/mb/AM3_PLUS_Ready/[dead link]
- Cebit: ASRock zeigt eine Reihe an AM3+ Mainboards mit alten Chipsätzen, PCTreiber.Net, 2011, retrieved 2012-01-10
|Wikimedia Commons has media related to: Socket AM3|
- Socket AM3 design specification (rev 1.06)
- DailyTech post about Socket AM3
- List of first bunch of Socket AM3 CPUs
- Socket AM3 review