AMD Radeon HD 7770 & 7750 Launch Review - PAGE 4

First up is the AMD HD 7770, which sports the Cape Verde XT GPU. This gives it slightly more power than the Cape Verde Pro GPU, as it comes packed with 1.5 billion transistors built on a 28nm node with a die size of 123mm² . Internally the core features 640 streaming processors, 16 ROPS and 40 texture units. The core clock speed is set at 1000MHz (1GHz)  giving the Cape Verde XT graphics card a total compute power of 1.28 TFLOPs. The HD 7770 also utilizes a 1GB GDDR5 fame buffer that is clocked at 1125MHz (4500Mb/s QDR), giving the HD 7770 has a total memory bandwidth of 72Gbps.

Turning to the visual style of the HD 7770, we can see it is similar physically to the Tahiti based graphics cards, but the PCB is dramatically smaller and the Cape Verde cards also adopt a propeller style fan design. While the card still uses the same red and black color scheme, the HD 7770 looks different from other Tahiti graphics as well as those from the previous generation Juniper series thanks to a centrally mounted fan. The HD 7770 does, however, include the same rounded shroud, which was designed to improve ventilation when the graphics card is being used in CrossFireX configuration. Also, since the PCB is smaller than the high-end cards, the HD 7770 measures in at just 8.25" which practically ensures the card that can fit into nearly any mid-sized chassis on the market.

The reverse side of the PCB includes a single CrossFireX connector, which indicates AMD is still only allowing their mainstream cards to be teamed in groups of two. In addition, the HD 7770 utilizes a PCIe 3.0 interface, and 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. However, since the HD 7770 is not a high-end graphics cards it will most likely not saturate the interface, even while running in CrossFireX.

The HD 7770 comes with a maximum PowerTune rating of 80 watts, so unlike Tahiti based graphics cards the HD 7770 does not require two power connectors. Instead it has a single 6-pin power connector at the tail-end of the PCB. This gives the board a total power capacity of up to 150 watts, which is a huge power buffer for overclocking. The HD 7700 series graphics cards also support "Zero Core Power". This reduces the load idle power consumption down to around 3 watts.

Looking at the stock video output configuration, we can see the HD 7770 features the same layout as the HD 7900 series. This gives the HD 7770 two Mini-DP 1.2 connectors, a single HDMI 1.4a connector and a Dual-Link DVI connector. The HD 7770 also uses the same non-stacked DVI design that was first introduced with the HD 7970. Essentially, this design improves the thermal performance thanks to improved heatsink ventilation. The non-stacked design also decreases the overall acoustics by reducing turbulence, making Southern Islands graphics cards quieter than the previous generation.. Also, just like the HD 7970, the HD 7700 will come bundled with a 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.

With the AMD HD 7770, AMD is continuing their improved Eyefinity and HD3D support. The card includes an HDMI port that uses the latest 1.2 standard, which allows it to support up to three monitors per port (via MST Hub) as well as AMD's 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, which makes viewing images and playing games smoother across the board. The HDMI and DP ports can also be paired together to support HD3D Surround.

Since the HD 7770 has a TDP below 100 watts, using a thermal solution similar to those on the Tahiti based graphics cards would simply be overkill. Instead, AMD has included a smaller oval shaped heatsink that has a large aluminum fin array and a centrally mounted propeller fan. Additionally, the base of the heatsink is custom designed to match the dimensions of the Cape Verde GPU, while the mounting brackets ensure the heatsink applies enough force to properly cool the core.

We really like this design, as it should get the job done and still be quiter than the traditional AMD thermal solutions that use a blower style fan. However, very few consumers will ever see this particular design, because most of AMD's AIB partners are going to release HD 7770 graphics cards with their own custom design and thermal solution.

The printed circuit board of the HD 7770 is considerably scaled down in comparison to the high-end models. Looking over the PCB we can see there are four HYNIX memory chips on the sides of the GPU in a 2 x 2 configuration, a front mounted 3-phase VRM, and eleven solid capacitors throughout the PCB. Most striking though is just how small the die size is. At just 123mm² it is impressive how AMD managed to squeeze in 1.5 billion transistors, so even while the performance will be mainstream the Cape Verde chips should offer a ton of performance per millimeter. In comparison to the 365mm² Tahiti GPU, the Cape Verde die has been shrunk by over 50%.