AMD is laying the foundation for its Socket AM3+, Bulldozer-based Zambezi processors with the 990FX chipset, functionally identical to 890FX. The big news is that motherboard vendors are licensing SLI again, and we want to compare performance to Intel.

Generally, platform reviews accompany new processors. But in the case of AMD’s 990FX chipset, there’s both good and bad news.

The good news is that AMD still has a fantastic compatibility story. So, 990FX supports today’s Socket AM3 processors and the upcoming AM3+ CPUs based on the Bulldozer microarchitecture.

The bad news is that those Bulldozer-based chips are still not ready. Processors based on the B0 stepping are in the hands of motherboard manufacturers. But they’re all telling me that performance is nowhere near what they were expecting, and it’ll take another stepping to fix them.

Technically, you could buy a 990FX-based motherboard today and drop in an existing Phenom II. But if you’re really lusting after a six-core Zambezi-based chip, it’d be better to simply wait a couple of months. Unless there was another reason to upgrade…

990FX: Same As 890FX, But Guaranteed Compatibility

The 990FX chipset employs the same silicon as 890FX. Didn't know today's launch was happening? Didn't know 990FX would be so similar to 890FX? If you were following me on Twitter, you would have! ;)

According to AMD, it’s incrementing the platform name to clarify compatibility with Bulldozer-based processors. When you see a board that centers on 990FX, the company wants you to know that its upcoming AM3+ CPUs are drop-in-compatible (again, 990FX-based boards will also take existing AM3 chips).

You need the 942-pin Socket AM3+ (AM3b) interface, though, in order to support Zambezi’s power and frequency management features.

Conversely, AM3+ processors also drop into Socket AM3 motherboards, given a BIOS update. Depending on the company that manufactured your AM3-enabled board, there may or may not be a firmware upgrade available immediately. So, understandably, AMD doesn’t want to leave the question of compatibility up in the air.

Even with a new firmware, though, you won’t get those aforementioned features on an AM3 platform. Also, 890FX and 990FX both support HyperTransport 3.0 with transfer rates of up to 5.2 GT/s. According to MSI, 990FX adds HyperTransport 3.1 support with signaling up to 6.4 GT/s (apparently something we’ll see from the eight-core Zambezis).

I’m not a fan of rebadging, but in this case, it’s a necessary evil. Sure beats murdering a processor interface every time you introduce a new architecture (*cough* Intel). Most enthusiasts will probably want to upgrade anyway to match Zambezi and AM3+. But it’s nice to know that AMD has its eye on the backward and forward compatibility of its processors and platforms.

SLI: A Pleasant Surprise

More pertinent than any AM3+ discussion, at least today, is the addition of SLI support on 990FX boards. Frankly, there’s nothing stopping the motherboard guys from licensing SLI on 890FX as well, but nobody I’ve talked to has plans to do that. Instead, it looks like SLI will be used as a differentiator to get gamers stoked about upgrading their processor and motherboard when the FX-series (Zambezi) chips launch.

As with Z68 Express, two-way SLI and CrossFire configurations are easily supported. AMD’s 990FX hits with 42 PCI Express lanes, giving each slot on a dual-card config its own 16-lane link (compared to Intel’s two x8 links). Don't get too worked up about this "advantage." Eight lanes is still enough for Intel's parts to compete aggressively. Don't believe me? Check out Thomas Soderstrom's three-part series on multi-card scaling.

Because 990FX boasts so much second-gen PCI Express connectivity, it doesn’t require NF200 to support three-way setups, though. Both of the 990FX boards that landed in our lab accommodate two- and three-way configurations (x16/x8/x8), along with quad-GPU arrangements using cards like GeForce GTX 590 and Radeon HD 6990.

Without AM3+ processors to test, today’s 990FX launch only has one really interesting angle: SLI-based performance using a Phenom II X4 980 versus Intel’s Core i5-2400, both configurations armed with a pair of GeForce GTX 570 graphics cards. The comparison couldn’t get any more even. Our P8Z68-V Pro sells for the same $210 Asus plans to ask for the Sabertooth 990FX, and the Core i5-2400 sells for $5 more than AMD’s Phenom II X4 980. With all other components equal, this is a true head-to-head.

So, is the return of SLI support to AMD’s chipset family worth an upgrade? Let’s find out!