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At the very end of the last year AMD introduced its new GPU codenamed Tahiti and one graphics card based on it. The card is called Radeon HD 7970 and supposed to be followed (presumably in February) by a less advanced and more affordable Radeon HD 7950.

Announced on the 22nd of December, the Radeon HD 7970 went on sale on the 9th of January only. And it is yet rather hard to find in shops. There are can be numerous reasons for that, from imperfections in the new 28nm tech process to transportation problems due to natural disasters. So we’ll put the availability issue aside for now, but will instead focus on the new Tahiti architecture and the first graphics card based on it.

GPU Architecture

The Tahiti processor belongs with the Southern Islands family which is comprised of three GPU models:

The Tahiti will be the heart of AMD's fastest and most expensive high-end cards: Radeon HD 7970 and HD 7950. The Pitcairn will go to mainstream solutions, the most popular choice among gamers. Named Radeon HD 7870 and HD 7850, these cards are expected to come about in February. And, finally, the name of Cape Verde is reserved for the low-end Radeon HD 77xx series which is supposed to replace the Radeon HD 67xx series.

AMD refers to the architecture of its new GPUs as Graphics Core Next (GCN):

Besides the expectedly increased graphics performance, the GCN architecture is optimized for computing tasks, so the Southern Islands chips feature Compute Units.

A non-VLIW Compute Unit combines vector and scalar subunits. Each GCN unit has a dedicated scheduler and can execute instructions from different programs. This multitasking orientation is a key feature of the GCN architecture at large.

The new cache memory subsystem includes 16 kilobytes of L1 cache per each compute unit and 32 kilobytes for storing instructions. The L2 cache is 768 KB large. This is 50% larger than in the Cayman processor (Radeon HD 6970/HD 6950).

The cache memory has become 50% faster: 2 terabytes/s and 700 gigabytes/s for the L1 and L2 cache, respectively.

The Tahiti incorporates an enormous 4.3 billion transistors (compare this to the Cayman’s 2.64 billion). It now has a total of 2048 unified shader processors. The GPU also has 32 raster operators and 128 texture-mapping units.

The GPU clock rate has grown up to 925 MHz. Combined with the rest of architectural improvements, it ensures a peak fillrate of 118.4 gigatexel/s. Thanks to the new 384-bit memory bus and high memory clock rate of 5500 MHz, the memory bandwidth is as high as 264 GB/s.

The ninth-generation tessellators are supposed to bring about considerable performance benefits, too.

AMD claims the tessellation performance is now 4 times that of the previous GPU generation but the diagram suggests that this is not true for all tessellation-using applications.

The quality of anisotropic filtering has also been improved.

Moreover, the anisotropic filtering improvements are not supposed to cause a performance hit on the new AMD Radeon HD 79xx series as well as other cards based on the Southern Islands family processors. The new GPU brings about a lot of architectural innovations, so we’ve only covered the key points. Let’s just move on to the more exciting things. We mean the new graphics card and its speed in benchmarks.

 
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