Nvidia GeForce GTX 680 review

AMD was first out of the gates with 28nm, but every Radeon HD 7000 Series card we’ve so far reviewed has come with a big caveat: wait and see what Nvidia does. Now the first 28nm “Kepler” chip is in our Labs, we can safely say we hope you heeded that advice – Kepler was worth the wait.

The GeForce GTX 680 is Nvidia’s new single-core flagship card, tweaked, refined and renamed from the “Fermi” architecture first launched with the GTX 480 in 2010. Graphics Processing Clusters, or GPCs, still form the building blocks of the new GPU, with each having its own resources for shaders, textures and compute processing. Each pair of GPCs shares a memory controller, but L2 cache is shared between all of the card’s GPCs.

While the GTX 480 and GTX 580 made do with 15 and then 16 GPCs, each with 32 stream processors, Nvidia is using only eight clusters on the GTX 680, each boasting 192 stream processors. That’s a huge increase, and closer to the 2,048 stream processors AMD includes in its flagship Radeon HD 7970.

Nvidia’s biggest new feature is something you won’t find on any AMD card: GPU Boost. With a nod to Intel’s Turbo Boost, it dynamically adjusts the core clock from the stock 1,006MHz depending on the operating conditions – ours idled at 549MHz, for example. When performance is required it adjusts the core every millisecond to try to hit the 195W power draw ceiling – ours rose to 1,097MHz. Nvidia claims this constant power draw makes for a more reliable card, as it’s fluctuations in draw, rather than a high level, that harm reliability.

The card has 2GB of GDDR5 memory running at 6,008MHz – almost twice the speed of the Radeon HD 7970 – but the 256-bit memory bus is narrower. The transistor count of 3.5 billion is slightly less than the 4.3 billion on the AMD card, but the GTX 680’s texture fillrate of 128.8GT/sec is higher than the 118.4GT/sec of the HD 7970.

That strength translates to strong benchmark results. In Crysis at 1,920 x 1,080 and Very High settings the GTX 680 averaged 70fps, 2fps ahead of the HD 7970. Both cards returned the same result at 2,560 x 1,600 – a playable 42fps.

The GTX 680 smashed the AMD card in Crysis 2. At 1,920 x 1,080 and Ultra settings – the toughest the game offers – it averaged 57fps, with the HD 7970 on 36fps. There was a sizeable gap when we upped the resolution, too, with the scores at 33fps and 26fps.