XFX HD Radeon 6790 ReviewRHKCommander959 - May 5, 2011
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The XFX HD Radeon 6790 is a mid-range offering developed off of the 6870 and 6850 technology. They all have Barts cores with the original core having 1120 Stream Processors, 56 texture units and 32 render units. The 6850 has part of the core disabled to lower the Stream Processors to 960 and 48 TMUs, while the 6790 is lowered again to 800 and 40 TMUs. All three cards have the same memory configuration of 1GB GDDR5 on a 256-bit memory bus and generally share all of the same features aside from clocks and core configurations. Even the board setup is similar on most of the cards out on the market.
AMD can control the amount of Stream Processors and texture units easily because they reside in clusters called Single Instruction Multiple Data blocks. These SIMD blocks each hold 80 processors and four TMUs. By disabling SIMDs AMD can cut back performance to fill market gaps. The stock Barts core has 14 SIMDs, disabling two groups creates the core for the 6850 and disabling another two is how the 6790 was created. With this method, AMD can bin the cores and take the less capable parts and disable groups to save cores and money while producing another product. According to AMD, the SIMDs have been fused off, so unfortunately BIOS flashing will not unlock them as was possible on some 6950s (if the news is true). The Barts core is built on the 40nm fabrication node at Taiwan Semiconductor Manufacturing Company, where AMD has had their GPUs made for quite a while rather than Global Foundries. The 6790 should have a low TDP. Two PCIe power connections are included on some cards but only to aid in overclocking as one is more than capable enough to power the card.
The top of the card shows that both fans are translucent gray. Adding in some LEDs would look nice for anyone into that. Two silver lines run the length of the card and add some flair. The XFX logo and card model are near the output side. The three heat pipes can be seen running along the top of the card. Flipping the card over shows the exposed backside. Two power connectors are side mounted at the rear and the card only has one CrossFireX connection near the output side. XFX has put two warranty stickers on the heat sink bolts that state removing them voids the warranty. These are spring loaded and the card is mid-range thus no back plate was used as is common for mid- and low-end cards. This is odd considering XFX use to be 'modder friendly' as their website still states.
The sides of the card are open. Air can escape from the front and back as well as the sides. This can cause system temperatures to climb as the card reheats prior exhaust air. In a system with good airflow it isn't a problem but others might have higher operating temperatures. Some side venting on the slot side is good to help cool the motherboard components. The other side has another XFX sticker with the model number on it. The heat pipes extend out with two under one fan and the other fan sitting partially over the heat sink base and the third heat pipe. Both the power connections and CrossFireX port are located on this side.
The output side has two DVI ports (one of which is labeled VGA and has limited output) two mini DisplayPorts, and an HDMI 1.4a port. The grill is a custom job with XFX machined into it. The HDMI port has a screw to reinforce it, to help keep it from breaking during usage. The I/O plate is also attached directly to the fan shroud with two screws, providing some rigidity. The rear of the card has 13 holes in the center for ventilation and two more for side access to the power ports and fan header. Hopefully consumers won't be paranoid over the 13-stigma. The two fans sit flush with the shroud meaning that using two of these in CrossFire could be dangerous as the four spring loaded bolts on the rear of one card could potentially jam and/or damage the fans. Not a likely scenario but very possible and worth mentioning.
Two 6-pin PCIe slots are installed on most of the 6790s, although some versions only have one. The power requirements are low enough that only one is really needed although some manufacturers have opted for the second connection to give enough headroom for high overclocking. These power connectors are side mounted. The card only comes with one CrossFireX connection in the standard location near the I/O panel, the design has been changed so older CrossFire dongles are not compatible anymore.
With the heat sink removed, the core is exposed in its entirety. AMD continues to use exposed cores on their GPUs with a shim to help protect them from cracking when the heat sink is installed. This method provides better thermal conduction over designs with integrated heat shields. The only problem with this design is when mated with direct-contact heat pipe coolers with rough bases (as is the case here). The memory is produced by Hynix, model H5GQ1H24AFR-T2C. These modules are clocked in at 1050 MHz with 128MB density each. These T2C versions are rated for 1250 MHz at 1.5V so they should have a decent amount of headroom! The base has been machined to be flat although the cut is rough, the gaps between the heat pipes is very noticeable and needs to be packed with thermal paste to improve conductivity. Generally, direct contact heat pipe coolers provide some of the best cooling. Four small screws attach the base plate to the fan shroud. Both fans are wired together and connect through a two-wire fan header at the rear of the card.
Time to check out the specifications and features before overclocking it!