| Type | PGA-ZIF |
|---|---|
| Chip form factors | PGA |
| Contacts | 941 (Socket)[1] 938 (CPU) |
| FSB protocol | HyperTransport 3.x |
| FSB frequency | 200 MHz System clock HyperTransport up to 3.2 GHz |
| Processors | Phenom II (AM3 models only) Athlon II Sempron Opteron 138x |
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This article is part of the CPU socket series |
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Socket AM3 is a CPU socket for AMD processors. AM3 was launched as the successor to Socket AM2+ on February 9, 2009, alongside the initial grouping of Phenom II processors designed for it.[2] The sole principal change from AM2+ to AM3 is support for DDR3 SDRAM.
The "AM3 Processor Functional Data Sheet" AMD document number 40778 has been made publicly available @ http://support.amd.com/us/Processor_TechDocs/46878.pdf
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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[1] 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.[3] 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).[4]
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,[5] Gigabyte,[6] 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.
AM3+ is a modification of the AM3 Socket designed for future "Zambezi" CPUs which use the new Bulldozer microarchitecture and will retain compatibility with AM3 processors.[7] The set of features is not yet known.[8]
An early preview of a motherboard from MSI[9], indicates Socket AM3+ is also known as Socket AM3b. The pin-count for this revised socket is 942-pins.
Some manufacturers have announced that some of their AM3 motherboards will support AM3+ CPUs, after a simple BIOS upgrade.[10] Mechanical compatibility has been confirmed and it's possible AM3+ CPUs will work in AM3 boards, provided they can supply enough peak current. Another issue might be the use of the sideband temperature sensor interface for reading the temperature from the CPU. Also, certain power-saving features may not work, due to lack of support for rapid VCore switching.[11] Note that use of AM3+ CPUs in AM3 boards may not be officially supported by AMD.
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