A recent announcement from Asus has thrown a wrench into this scenario. We've reached out to both Asus and AMD for additional information; neither has gotten back to us as of this writing.
Asus' website states:
Current owners of an AM3-based board* will make their AMD 8-Series motherboards compatible with the latest AM3+ CPUs with a simple BIOS** update from the official ASUS website... Current ASUS 890FX and 890GX series motherboards can be upgraded to enjoy the extra performance offered by future AM3+ CPUs (emphasis added). ASUS will also be releasing*** the AMD 8-Series Chipset motherboards based on 880G and 870 as well as the 760G Chipset on the AM3+ socket for increased selection so users can enjoy AM3 and AM3+ CPUs.There's precious little wiggle room in Asus' statement and there's no way the company could be referencing Llano—that chip, when it appears, will use AMD's Socket FM1. The state of AM3+ CPU support in existing motherboards has never been less clear. Up until now, the preponderance of evidence suggests that the AM3+ socket is physically different from the AM3 socket.
** Current BIOS update is a beta release. Please check the ASUS support site for continual updates.
That's AM3 on the left, AMD3+ (purportedly) on the right. Original photographer unknown.
Look at the stanchion that's circled in both images. The AM3 socket blocks off two pins while the AM3+ socket blocks off just one pin. In theory, this explains why AM3 chips can work in AM3+ motherboards but not vice versa.
One of the motherboards Asus' lists as supporting AM3+ is the Crosshair IV Extreme. We recently reviewed that board, noting that "If existing AM3 products were Bulldozer-compatible and LucidLogix's game support was more mature, this motherboard would be a must-have for any AMD enthusiast..."
Actual Bulldozer support on the Crosshair IV Extreme would be a Very Big Deal, but a quick check of our testbed proved that the board isn't harboring an AM3+ socket in disguise.
The Crosshair IV Extreme's CPU socket. Note that the space in the upper-right-hand corner blocks off two pins, not one
Check the upper-right corner (outlined in violet) and you'll see that the gap is sized for an AM3 rather than an AM3+ processor. With AMD saying that AM3+ processors won't be supported on AM3 boards, Asus saying it can grant such support in a BIOS update, and a physical difference between the sockets, the upgrade situation has gone murky in less than a week.
Absent any input from AMD or Asus, we've put together a short list of potential explanations.
Asus never mentions Bulldozer by name on its webpage and refers only to "extra performance offered by future AM3+ CPUs." Back when AMD released its original AM3 processors, a number of manufacturers (including Asus) took to labeling AM2 boards as offering AM3 support. We know AMD will continue to sell Phenom II processors after Bulldozer launches; Asus may simply be noting that an AM3+ Phenom II will fit into an AM3 socket without referring to Bulldozer at all. At present this seems the most likely scenario--it explains why Asus doesn't mention Bulldozer on its announcement page. Unfortunately it also invites confusion—AM3+ Phenom II's would end up working in AM3 boards while AM3+ Bulldozer's would be restricted to AM3+ boards.
Another option is that AMD will release a series of AM3-compatible Bulldozers. The company has done this before—it continued to release Socket 754 chips up through the launch of Socket 939—but AMD also publicly committed to supporting the Socket 754 platform before and after it launched. AMD's John Freuhe is on record at multiple forums stating that AMD will not "support" Bulldozer on AM3, but the word "support" can be quite fluid.
Third, it may be possible to modify a Bulldozer chip (by presumably removing that single extra pin). This would theoretically make Bulldozer pin-compatible with the current AM3 socket and explain why AMD would never support such a configuration. Asus' claim that a board needs nothing more than a BIOS flash to be AM3+ compatible, however, strongly implies no major chip surgery will be required.
Fourth, it's possible that AMD is pulling an Intel with regard to new chipsets. The pin that (presumably) plugs into the now-vacant hole in the upper-right-hand of an AM3+ socket could be relatively spurious; the company might simply want to sell fresh chipsets. . Again, however, this doesn't really track. Asus pointedly notes that it's launching a series of motherboards based on AMD's 880G and 760G chipsets--not something the company could do if AMD's older chipsets weren't capable of detecting and running AM3+ processors.
At this point we're guessing that Asus' is referring to future Phenom II-based products that will launch on Socket AM3+ rather than anything Bulldozer-related. It'd be fabulous if Asus can offer Bulldozer on even some of its AM3 boards, but until the company states that it's explicitly referencing the next-gen processor, we're assuming it isn't. It makes more sense that AMD would move Phenom II to AM3+ the same way it released AM3 versions of AM2+ processors a few years ago.