Advanced Micro Devices said that its next-generation desktop processors code-named Zambezi will use socket AM3+ platforms, which will be backwards compatible with the firm's existing AM3 products. While the latter is an advantage for the platform, it may be a disadvantage for eight-core processors based on Bulldozer micro-architecture.
"The existing G34 and C32 server infrastructure will support the new Bulldozer-based server products. In order for AMD's desktop offering to fully leverage the capabilities of Bulldozer, an enhanced AM3+ socket will be introduced that supports Bulldozer and is backward-compatible with our existing AM3 CPU offerings," an official from AMD said in an interview with Planet3DNow web-site.
Apparently, it was possible for AMD to make Bulldozer microprocessors compatible with existing AM3+ infrastructure, but in order to do that, the company would have to sacrifice certain important features of the new core.
"When we initially set out on the path to Bulldozer we were hoping for AM3 compatibility, but further along the process we realized that we had a choice to make based on some of the features that we wanted to bring with Bulldozer. We could either provide AM3 support and lose some of the capabilities of the new Bulldozer architecture or, we could choose the AM3+ socket which would allow the Bulldozer-base Zambezi to have greater performance and capability," the official said.
The compatibility with older microprocessors allows AMD to simplify transition to the new micro-architecture and process design since the new AM3+ platform will support inexpensive chips from day one. However, such compatibility also means that AMD Zambezi processors will only support dual-channel memory controller. Considering the fact that all modern high-end Intel Core i7 processors with up to six cores feature triple-channel memory controller, it is unclear how AMD plans to "feed" eight cores of Zambezi with dul-channel DDR3 without creating bottlenecks.
AMD Bulldozer-based processor code-named Zambezi will have up to eight cores along with a new TurboCore dynamic acceleration technology. Thanks to the new micro-architecture the chip promises to be faster than existing AMD products.
Source: Desktop Bulldozer Processors Will Require New Platforms - AMD - X-bit labs
Basically you can use AM3 processors in a AM3+ socket but you cannot use a AM3+ cpu in a AM3 socket. This also means Bulldozer will be dual channel DDR3 which may be a problem seeing as lga2011 Sandy bridge processors are rumored to have Quad channel memory.
I'm glad I didn't jump on the AM3 bandwagon since the platform will be so short lived.