PowerColor HD 6790 ReviewRHKCommander959 - April 4, 2011
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The new AMD Radeon HD 6790s are all Barts cores with some rendering capability scaled back. They have 800 Stream Processors: 10 Single Instruction, Multiple Data (SIMD) blocks enabled whereas the 6850 and 6870 have 12 and 14 enabled respectively. Each block has 80 Stream Processors and four texture mapping units (TMUs) per SIMD. The card retained the 32 Raster Operation Processors of the Barts core. The core was built at Taiwan Semiconductor Manufacturing Company (TSMC) on their 40nm fabrication node, this design was originally intended to be built at 32nm but TSMC chose to cancel the process. The memory bus is 256-bit with the 1GB of GDDR5 of memory clocked at 1050MHz has a bandwidth of approximately 134.4 Gb/s, this is pretty high considering the card is in the very middle of the 6-series AMD design.
The PowerColor Radeon HD 6790 has three outputs: one mini DisplayPort, one HDMI, and one DVI port. The box also included a VGA adapter so four different standards are supported out of the box. The top of the card has two stickers on it, to the left is the PowerColor brand and to the right is the card type along with the knight from the box art. The whole device is a fan shroud, the center holds the fan impeller that is nearly as wide as the card. Some of the heat pipes can be seen underneath as well. The back side is empty of large electronics, several spots have been left out: there is room for a second mini DisplayPort and DVI output, another 6-pin PCI Express power connection, and several capacitors and so on are missing. The card is likely a 6800-card that was lowered down. The card only has one CrossFireX slot, in the same location as always. AMD made the slot differently than the older generations, and the box didn't contain a CrossFireX dongle, something to be aware of!
The side shots show some of the capacitors and chokes hiding underneath the heat sink, you can also see the three heat pipes centered over the GPU core. The design of the shroud allows the card to receive air easily even when butted up to another card. Back when computers started having multiple cards, some manufacturers made the mistake of not giving enough space around the blower motor or fan to intake air when sandwiched next to another card and temperatures would climb dangerously as the card suffocated!
The front of the card features three outputs: mini DisplayPort, HDMI, and DVI. Above these is an exhaust grill to help get some of the heated air out of the case, however the design blows air in every direction, mainly to both ends of the card so only some air will exhaust out of the case. Having a positive pressure air design in the case will help ventilate more. The rear of the card is where the power connector resides, the three pin fan connection is nearby as well.
The base of the heat sink is rough but adequate for the job, it is flat enough. Four screws at opposite ends of the base plate attach to the shroud and hold the two together. Four standoffs are used to mount the heat sink to the graphics card via screws with springs attached to provide adequate mounting force while not bending the PCB nearly as much as they would without them. Still not as secure as a back plate but they'll suffice. Looking at the GPU-side of the card you can see several electronics missing. To reiterate, this was probably a 6800-series card that got chopped down to help fill the market gap. The core is rectangular and mounted roughly 45° offset with the card. Eight GDDR5 memory ICs from Elpida provide the card with 1GB of memory, the card uses a 256-bit memory bus to connect through. The card should see around 134.4 GB/s memory bandwidth, not too shabby for a mid-range card.
The 6790 Barts LE core is produced at Taiwan Semiconductor Manufacturing Company (TSMC) on their 40nm fabrication process, originally this series was intended to be launched on a 32nm process but TSMC cancelled. The next series should be produced on 28nm technology. The Barts core has a die size of 255 mm² and roughly 1.7 billion transistors. The 6790 has had 4 SIMD cores disabled to lower its performance enough for the mid-range market, it still has 32 ROPs, 40 TMUs, and 800 Stream Processors. It may be possible to unlock the extra cores if AMD has only employed a BIOS lock, although additional modification would likely be needed to make this card stable since it only has one 6-pin power connection and would likely draw too much power. The memory was provided by Elpida this time around and uses 1.5V, the model number is EDW1032BABG.
Time to take a look at the features!