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Socket AM3 Platform

By introducing new Socket AM3 platform, AMD is first of all trying to bring contemporary DDR3 SDRAM into Phenom II based systems. The competitor’s platforms have supported this memory type for more than 1.5 years, but AMD believed it wasn’t the right time for transition because of high price on DDR3 SDRAM. Now the situation has changed dramatically, DDR3 SDRAM prices dropped. This pushed AMD to introduce the new processor socket to the market.

However, unlike their primary competitor, AMD have been very reluctant lately to make any serious changes to their platform design.  Company engineers did everything they could to ensure the most painless migration from one platform to another. This is especially important in the today’s state of things, when AMD processors do not have as many advantages as Intel solutions. This is exactly why the new platform is so interesting: AMD developers managed to upgrade the memory controller built into their own processors in such a way that neither old nor new fans of the Athlon and Phenom brands would be disappointed.

A quick glance at new mainboards and processors is more than enough to understand that Socket AM3 platform is very similar to its predecessor. AMD didn’t switch to using LGA packaging for their chips; moreover, their processors remained of the same geometrical size and the number of pins remained almost the same. Thanks to the fact that AMD focused on continuity and compatibility, only a real close look will allow telling Socket AM3 processor from its Socket AM2+ counterpart.

Left - Socket AM2+ CPU; right – Socket AM3 CPU

You can only see the differences between Socket AM2+ and Socket AM3 processors at the bottom of the CPU. The photo above shows that Socket AM3 processor has 2 pins less, i.e. has a total of 938 pins.

You can notice the same if you compare the processor sockets on the mainboards:

Left - Socket AM2+; right – Socket AM3

As you can see, the mechanics of Socket AM3 processors allows installing them into Socket AM2+ mainboards. However, Socket AM2+ processors will never fit into Socket AM3 mainboards because of the notches location in the socket. This mechanical compatibility reflects the logical compatibility. New Socket AM3 processors have a universal memory controller that supports DDR2 as well as DDR3 SDRAM. The type of memory in each particular case is determined solely by the type of DIMM slots laid out on the mainboard. Socket AM2+ mainboards are equipped with DDR2 DIMMs, while Socket AM3 mainboards – with DDR3. Older Socket AM2+ processors cannot boast the same universality and can work only with DDR2 SDRAM that is why they are mechanically incompatible with the new processor socket.

Socket AM2+ and Socket AM3 remained successors in many other aspects. Since the size of processor sockets and processors themselves is the same, AMD could make sure that the same processor coolers can be used on both platforms. Even the retention mechanism remained unchanged.

The same is true for the microarchitectural peculiarities: Socket AM2+ and Socket AM3 CPUs differ only by the memory controller. All other components, including the HyperTransport 3.0 bus remained unchanged. And it means that Socket AM3 platform doesn’t require new chipsets, because these processors are perfectly compatible with the same core logic sets as Socket AM2+. Therefore, the major developers of chipsets for AMD platform do not offer any special solutions targeted for the new processors.

Almost complete mechanical and logical compatibility between the two types of CPU sockets sometimes allows veering away from the following equivalence: Socket AM2+ – DDR2 SDRAM, Socket AM3 – DDR3 SDRAM. Some mainboard makers, Jetway for example, prepare universal Socket AM2+ mainboards equipped with DDR2 and DDR3 memory slots at the same time. These mainboards with a  Socket AM3 processor installed will allow using either memory type.

Socket AM3 processors officially support DDR2 memory with up to 1067MHz frequency and DDR3 memory with up to 1333MHz frequency. Moreover, DDR3-1333 SDRAM is guaranteed to work stably and reliably in Socket AM3 systems only if there is no more than one module per channel installed. However, in reality it turns out that the new processors can also work with DDR3-1600 SDRAM: the built-in controller supports the corresponding multiplier for this frequency. Namely, when you install a Socket AM3 processor into a Socket AM2+ mainboard, you can choose from the standard memory frequencies for any Phenom processors: DDR2-667/800/1067. However, if you use it with a Socket AM3 mainboard, you are offered a different list of supported multipliers that allow clocking the memory as DDR3-1067/1333/1600 SDRAM.

Here I would like to add that to ensure full compatibility of Socket AM2+ mainboards existing in the today’s market with the new Socket AM3 processors, all you need to do is reflash the BIOS. If the mainboard BIOS supports Phenom II processors altogether, even their Socket AM2+ version, it automatically means that Socket AM3 processors will also work in this board just fine. And it means that there shouldn’t be any problems adapting the existing mainboard inventory for the new processors.

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