AMD Radeon HD 7970 Launch Review - PAGE 4

The "Tahiti XT" GPU is designed to fit into the enthusiast market and sits above all other single GPU graphics cards currently available. AMD is also going to release the "Tahiti Pro" graphics processor at a later date, but for the time being it is still being kept behind closed doors. Later down the line, AMD is also going to be releasing "Pitcairn" (to replace the HD 6800 series) and "Cape Verde", which is the Southern Islands budget GPU.

Aesthetically, the HD 7970 is best described as a hybrid between the HD 5000 and HD 6000 series graphics cards. As you can see, the HD 7970 still sports the classic AMD red and black color scheme and uses a rear mounted blower style fan, but the shroud has a more rounded design. The new visual style is actually quite appealing in comparison to the VHS design of the HD 6000 series. Along with the improved look, the rounded design of the back-end of the shroud improves ventilation when the graphics card is used in CrossFireX. As far as the dimensions go, the HD 7970 is roughly the same size as the HD 6970, so even with the reduced die size the PCB is still 10.5-inches in length.

The "Tahti XT" core itself is built on a 28nm process with a die size of 365mm² and has roughly 4.31 billion transistors. With the smaller node, AMD was able to turn up the engine to 925MHz, while still including 2048 streaming processors, 32 ROPS and 128 texture units, giving the card a total compute power of 3.79 TFLOPs peak single precision FP and 947 GFLOPs of double precision. Additionally, the HD 7970 comes with a massive 3GB GDDR5 fame buffer clocking in at 1375MHz (5.5Gbps QDR) and running on a 384-bit memory bus. This gives the HD 6970 substantial memory bandwidth but since most games are not memory limited, the biggest impact on performance should be seen when using the graphics cards Eyefinity or HD3D technologies.

The back of the PCB is clean for a high-end graphics card, but all the solder points give away some of the card's secrets. Looking at the back of the board, we can see twelve soldering points for the memory that surround the GPU in a C-shaped pattern. Interestingly enough, the board includes solder points for two full 8-pin power connectors. We aren't entirely sure what AMD was working on there, as that would given the board a total power rating of 375W which far higher than any single GPU graphic card currently on the market.

The back also includes two CrossFireX connectors and a PCIe Generation 3.0 x16 lane.  By using the PCIe 3.0 interface, the board has double the maximum data rate over Gen 2.0, giving the card up to 32 GB/s of bi-directional bandwidth on an x16 connector. It is going to be hard for a single graphics card to saturate the PCIe Gen 3 interface with so much bandwidth, so the benefit will most likely only be noticeable with scaling multiple graphics cards together in CrossFireX configuration.

Like the 6900 series, the HD 7970 comes equipped with PowerTune technology. PowerTune is basically a power management system that maximizes the performance of the board via dynamic power adjustment. It does this by increasing the GPU clock speed in real time when the GPU detects power headroom, and throttling the clocks when a certain power limit is exceeded. This allows the board to adjust the clock speeds on a microsecond level. The maximum PowerTune rating for the HD 7970 is around 220W at load, but even with a power envelope lower than the HD 6970, AMD has included a  8+6 pin power configuration for up to 300W of power. This gives the board plenty of headroom which should come in handy during overclocking, and also ensures the board is fully stable during peak power consumption.

With the 28nm node we were expecting the power consumption to be slightly lower than 220W, but even so AMD has still managed to impress us with the board's idle power features. What they have done is added a feature called "Zero Core Power Technology" that reduces the idle power consumption by up to 95%. This allows the graphics card to reduce the power down to around 3 Watts when the system is idle for long periods of time, whereas a standard idle period has a power consumption rating of 15W. At both idle and long idle, the board utilizes a GPU clock deep sleep and DRAM stuttering features, along with compressing the contents of the frame buffer. This gives the HD 7970 roughly a 45% improvement in idle power consumption in comparison to the HD 6970.

One of the most interesting features of "Zero Core Power" is seen when using CrossFireX. Traditionally, anyone using multiple GPUs in a single system had to deal with a high power idle state, simply because each card was still actively drawing system power; each graphics card could produce 30+ watts of power even when the system wasn't under load. With "Zero Core Power", the extra graphics cards in a CrossFireX system are disabled, shutting down the fans and capping any voltage from going to the core. Since PowerTune works on a microsecond level, "Zero Core Power" will not interfere with gaming as all the GPUs can become active again in microseconds.

The default video outputs on the HD 7970 are similar to the 6000 series. In total there are two Mini-DP connectors, a single HDMI 1.4a connector and a Dual-Link DVI connector. Noticeably missing however is the stacked DVI port that was first introduced with the 6800 series graphics cards. The reason behind removing the port is not due to a substantial change in the video configuration, or even the MST Hubs becoming available. Instead AMD explains that removing the second DVI port actually reduces the level of turbulence being created, thus decreasing the overall acoustic levels during operation. Each HD 7970 will also ship with an HDMI to DVI dongle, and mini-DP to DVI dongle that allow the card to support up to three DVI connections out of the box.

The two on-board Mini-DP ports use the 1.2 standard which allows them to support up to three monitors per port (via MST Hub) and also support AMD HD3D technology. The middle HDMI 1.4a connector also supports 3GHz speeds with frame packing. Essentially this allows the connection to run the frames faster, thus creating a smoother gaming experience. The HDMI and DP ports can also be paired together to support HD3D Surround which increases both the depth and field of view in games, making for a truly unique gaming experience.