High-Tech Hot Potato: AMD, Asus Clam Up On AM3 Compatibility Questions

Two weeks ago, we discussed Asus' claim that certain AM3 motherboards would function properly when paired with AM3+ processors. We've since spoken with both companies and have a (slightly) clearer idea of what to expect. Asus' announcement is not, in any way, a refutation of AMD's previous comments on Bulldozer support. According to Sunnyvale, Bulldozer will only be supported on AM3+ motherboards.

AMD directed all other questions to Asus while Asus, once we spoke with them, informed us that they were under NDA not to discuss any details of their previous announcement. We were, however, able to learn a few additional tidbits of information. Previously, we noted that AMD could theoretically transfer Phenom II CPUs to AM3+. It's still unclear why Asus didn't simply refer to 'Bulldozer' in its previous announcement, but there's little chance it was referring to a current product on an AM3+ platform.

It looks like the Crosshair IV Extreme will support AM3+ products, if only unofficially

We previously speculated that AM3 and AM3+ CPUs might be physically different in a way that would prevent the latter from plugging into the former socket. This isn't the case--while the socket differences we noted in our previous article exist, they don't appear to define compatibility.

The situation appears to be as follows:  Some AM3 motherboards, including all of the boards Asus lists as compatible, will support a drop-in Bulldozer upgrade once the BIOS is properly flashed. The nature and degree of said support is unknown. Those who plug an AM3+ CPU into an AM3 board will lose certain features. These are almost certain to be related to power conservation or clock gating; high-speed enthusiasts might never notice the difference.

It may not be a great idea to bet on AM3+ CPU support if you already have an AM3 motherboard. One thing AMD did point out is that it has no control over what various vendors do or do not cover. Even when AMD officially declared that Phenom II processors would be drop-in replacements for original Phenoms, some motherboard vendors neglected to provide BIOS updates. The state of support in an unofficial upgrade situation could well be more tenuous.

In this case, high-quality AM3 boards based on older chipsets may still be able to get in on the action. Asus' chipset comments in its original press release indicate that there's nothing to prevent older chipsets from functioning with a Bulldozer core as opposed to a Phenom II. Again, we'll have to wait and see; motherboard manufacturers aren't falling all over themselves to announce their own boards are just as compatible as Asus'.

Enthusiasts who want a board that they absolutely know will support Bulldozer flawlessly will need to pony up for an AM3+ products. Everyone else will have to wait and see how the dice fall. With a Crosshair IV Extreme already in hand, we plan to test the upgrade theory once Bulldozer products launch and are reviewed on their intended AM3+ platforms.