Questions of Compatibility: AMD, AM3, and Bulldozer

Introduction To AM3+ Compatibility

It's been several weeks since Asus announced that certain socket AM3 motherboards would support AMD's upcoming Bulldozer processors. Since then, we've turned up additional rumors on the nature of such support. MSI has also announced its own plans to retrofit some existing AM3 boards with Bulldozer compatibility. What follows is the general shape of the situation as we currently understand it.

Will AMD Officially Support Bulldozer On The AM3 Platform?

No. The recent announcements from Asus and MSI make it clear that some AM3 boards will function with a Bulldozer-class processor installed. With that said, AMD originally justified moving from AM3 to AM3+ because not doing so would prevent certain Bulldozer features from functioning. AMD has not specified which features are affected yet; it's our belief, based on conversations with people in the know, that Bulldozer's advanced power management and clock gating capabilities require an AM3+ socket.

Gigabyte has also announced a new line 16 "Black Socket" boards that are AM3+ ready

What's The Difference Between Unofficial and Official Support?
Quite a bit. For one thing, "unsupported" is almost always code for "voids your warranty." Official support doesn't automatically translate into practical compatibility. AMD has officially supported two separate product introductions in recent history. First, all AM2 boards that supported Phenom officially supported Phenom II. Second, all AM2+ boards officially supported AM3 processors. In both cases, actual compatibility implementation was left in the hands of the motherboard manufacturers.

There are occasionally cases where neither official support nor proper BIOS implementation is sufficient. AMD's 780G chipset, which launched to considerable acclaim, was capable of supporting AMD's entire range of processors. It soon became apparent, however, that a number of mATX 780G  boards were incapable of handling AMD's 125W Phenom processors. Well-built boards using high-quality components had no problems. The rest were quickly restricted to 95W TDPs or less.

Asus' Crosshair IV actually *will* support Bulldozer. It's a fact that could significantly improve the board's marketability—if we knew more about the nature of that support.

What Have Asus / AMD Said?

AMD has officially said that it will support Bulldozer with the Socket AM3+ infrastructure. Questions regarding Bulldozer and AM3 support should therefore be directed to the motherboard manufacturers in question*. We attempted to talk to Asus, but were told that the company will no longer be talking publicly about AM3/Bulldozer support, at the request of AMD. Thus, Asus was unable to talk to us about the specifics of its own product based on an announcement it had already made.

What's The Bottom Line?
Some AM3 boards will support Bulldozer processors. The characteristics of that support and the degree to which performance, power consumption, and thermals will be affected is unknown. We generally expect that more expensive, enthusiast-class boards will offer a greater degree of support than bargain-basement models. Similarly, companies are more likely to update newer, better, boards than older ones.

The rumor mill indicates that multiple AMD chipsets will be capable of supporting Bulldozer. There's scant info on just how much various companies will implement support on older boards. Expect actual compatibility to vary considerably. The nature of this situation makes it very likely that some boards that should support Bulldozer, won't. Others may not be able to deliver power adequately given the CPU's different requirements.

The best thing to do is wait and see. We'll have to wait for launch to see what disparities exist between AM3 and AM3+ features and performance. We expect other motherboard manufacturers will make their own announcements about AM3 compatibility in the weeks ahead, but in lieu of the unofficial nature of support, we recommend waiting as opposed to buying a board now with a plan to drop an AM3+ processor in it.

*At the time this article was written, only Asus had announced that Bulldozer would be supported on AM3.
Multiple vendors have since made similar statements.

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