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The one card: Radeon HD 7970
We've discussed Tahiti's improvements in key graphics specs versus Cayman, but AMD has another bit of good news in store, too. Onboard the Radeon HD 7970, Tahiti will flip bits at pretty good clip: 925MHz. That's up slightly from the highest default clocks for products based on Cypress (the 5870 at 850MHz) and Cayman (the 6970 at 880MHz). The 7970 has the same 5500 MT/s memory speed as its predecessor, so it will rely on 50% more memory channels to provide additional bandwidth.

The 7970's combination of clock speeds and per-clock throughput give it the highest theoretical memory bandwidth, texture filtering rate, and shader arithmetic rate of any single-GPU video card. Thus, AMD has taken direct aim at Nvidia's single-chip flagship, the GeForce GTX 580, by pricing the Radeon HD 7970 at $549. That price will get you a card with 3GB of GDDR5 memory onboard, enough to drive multiple displays at high resolutions, and it undercuts the 3GB versions of the GTX 580, which are selling for just under $600 at Newegg right now. AMD says it is shipping cards into the channel now, and the plan of record is for formal availability to start on January 9th. We wouldn't be surprised to see cards for sale before the official date, though, if they make it to the right retailers.

Left to right: Radeon HD 5870, 6970, and 7970

At 10.75", the 7970 matches the length of its two predecessors almost exactly. However, the deletion of one DVI port has opened up additional real estate on the expansion plate cover for venting. This change, along with the use of a somewhat larger blower pushing air across the card's vapor chamber-based cooler, should improve cooling efficiency and allow for more air movement at lower fan speeds—and thus lower noise levels.

The downsides of this config are all related to the removal of that DVI port. What remains are two mini-DisplayPort outputs, an HDMI port, and one dual-link DVI output. To offset the loss of the second DVI port, AMD is asking board makers to pack two adapters in the box with every 7970: one HDMI-to-DVI cable and one active mini-DP-to-DVI converter. That config should suffice for folks wanting to run a three-way Eyefinity setup on 1080p displays or the like, but I believe neither of those adapters support dual-link DVI, so folks hoping to drive multiple 30" monitors via DVI may have to seek another solution.

Incidentally, like the 6970 before it, the 7970 should in theory be able to drive as many as six displays concurrently when its DisplayPort outputs are multiplied via a hub. Unfortunately, the world is still waiting for DisplayPort hub solutions to arrive. AMD tells us it is working with "multiple partners" on enabling such hubs, and it expects some products to arrive next summer.

Although the 7970's clock speeds are fairly high to start, AMD claims there's still quite a bit of headroom left in the cards and in their power delivery hardware. The GPUs have the potential to go over 1GHz, with "a good chunk" capable of reaching 1.1GHz or better. The memory chips, too, may be able to reach 6500 MT/s. In addition to giving end users some healthy overclocking headroom, that sort of flexibility could allow AMD's board partners to build some seriously hopped-up variants of the 7970.