We should all remember the 22th of December when the latest AMD Radeon HD 7900 series has been launched, starting with the HD 7970 card. The GPU takes part from the Southern Islands family made on 28nm process: Tahiti, Pitcairn and Cape Verde, each aimed at a different performance segment.
The new architecture is called GCN (Graphics Core Next) and is a step forward regarding graphics and computing capabilities.
The Tahiti series is aimed at high end enthusiasts, packed with compute units and a 384-bit memory interface, enough to drive the latest games at high resolutions.
The RADEON HD 7970 GPU has 32 compute units, for a total of 2048 individual stream processors. Each board comes with 3GB of high-speed 5.5Gbps GDDR5, hooked up to the 384-bit memory bus to offer an outstanding 264GB/s bandwidth. This kind of engine and memory bandwidth calls for a lot of data, and this is where the PCI-Express 3.0 interface becomes important.
The PowerTune feature puts the GPU in control and it can push its clock to fill up that thermal headroom when it is available. This technology was introduced at the Radeon HD 6900 series and became a standard on the 28nm lineup.
PowerTune is a integrated on-die system of two microcontrollers by which the GPU can calculate its power consumption at any given time and adjust its clock speeds up or down if it detects power headroom (or lack thereof).
The Southern Islands family is the first to use a Zero Power Long Idle state, which we have also described in the previous HD 7770 and HD 7750 reviews. Long Idle is what your system does when you leave it on and walk away, if we leave our system overnight, or even if you go to the bathroom and Windows turns your display off after a few minutes.
When the driver has got the signal that the display has gone black, voltage to the 3D core is cut and also to the memory controller; AMD puts the GDDR5 into a self-refresh mode, they cut voltage to all the display engine and gets us down to a GPU power of less than one Watt or about 2-3W at the board.
The only thing that is kept alive is the PCI-Express interface, used to jump-in and out of this state in milliseconds. This system is also perfect from CrossFire configurations; with Zero power, in a 4-way multi-GPU system, each of the slave cards will drop into a BACO state and go to sleep until they are needed; this means that we can have our 4-card system idling at about 20W of GPU power, less than a single Cayman.
At default, the Radeon HD 7970 will run at 925MHz for the core and 5.5Gbps on the memory. Recently, the higher clocked GHz versions made their way to the market, named GHz editions, meant to blow away the competition.