Asus Direct CU II Radeon HD 7790

The Asus Direct CU II Radeon HD 7790 is a new mainstream graphics card based on AMD's Bonaire GPU. Bonaire is a new chip?the other two members of the HD 7700 family, the 7750 and 7770 use a graphics core known as Cape Verde?but it's not a new architecture. Bonaire uses the same Graphics Core Next architecture that powers the rest of the HD Radeon 7700 to 7900 cards. It's rare for a company to re-spin a budget GPU on the same architecture and process technology. According to AMD, there was a performance gap between the 7800 and 7700 product families that HD 7790 is meant to address. At present, the HD 7770 GHz Edition family of cards starts at roughly $109, while HD 7850 cards are around $179. With a $149 base, the HD 7790 is meant to drop neatly in between these two cards.

Design and Features

The HD 7790 has 40% more stream processors (896 vs. 640) and texture units (56 vs. 40) than the HD 7770. It can handle two primitives per clock instead of the 7770's one, which doubles the card's potential geometry throughput. The total number of raster operator units (ROPs), however, remains steady at 16. That puts a hard limit on the card's pixel fillrate, which remains capped 16 gigapixels (GP) per second.

The 7790's other major improvement over the HD 7770 is its memory bandwidth. Both cards use a 128-bit memory interface, but the HD 7790 ratchets up its memory clock to a blistering 1500MHz (6GHz effective data rate). Total bandwidth is 96GBps, up from the HD 7770's 72GBps.

The other new feature of the HD 7790 is the card's enhanced overclocking technology (AMD PowerTune). Previous HD 7700 to HD 7900 cards have had four distinct states, each with a different clock speed, voltage, and power consumption target. The HD 7790 has eight states and switches between them more quickly. Unlike Nvidia, which recently switched to temperature-based overclocking with the GTX Titan video card, AMD's new PowerTune tech is still based on TDP.

That's the new GPU in general. The specific card we've tested is the Asus DirectCU Radeon 7790 GPU with 1GB of RAM (AMD says to expect a mixture of 1GB and 2GB cards on the market). The card ships with a default 1,075MHz clock, which is a tad higher than the 1GHz AMD specifies. Memory clock speeds are also higher, at 1600MHz (6.4GHz effective clock rate). The DirectCU II OC uses a dual-fan design with a heatsink + fan configuration that's actually longer than the card it covers. Up to four displays are supported (HDMI, 2x DVI, and DisplayPort).

We tested the card on an Intel DZ77GA-70K motherboard with an Intel 3770K CPU and 8GB of DDR3-1600. Windows 7 64-bit w/ SP1 and all available patches was used.

Performance
Since AMD decided to launch the HD 7790 on extremely short notice, we've got fewer test results than we'd otherwise prefer, and they're split between the HD 7770 and the Nvidia GTX 660. The GTX 660 isn't Nvidia's comparable product in this market; the cheapest card at NewEgg is $214. That's well into HD 7850 / HD 7870 territory and $65 above the HD 7790's $149 MSRP. Our Nvidia figures, therefore, will be presented for reference only.

Our first set of benchmark tests, in older titles, show that the HD 7790 is a worthy upgrade to the HD 7770. Aliens vs. Predator, DiRT 3, and Just Cause 2 were all btest at 1,680-by-1,050 resolution with all details set to maximum. The first two titles include their own benchmark utilities; our Just Cause 2 test used the "Concrete Jungle" benchmark map. The HD 7790 is 26% faster in Alien vs. Predator (32.8 fps vs. 26.1 fps) and 40% faster in DiRT 3. (64.7 fps vs 42.6 fps). In Just Cause 2, the Asus Direct CU II 7790 hit 43.23 FPS compared to 29.9 FPS for the standard HD 7770?a gain of over 40%.

The gap between the Nvidia GTX 660 and HD 7790 at 1,920-by-1,080 and in newer titles is still significant. In Civilization V's Late Game View benchmark, the GTX 660 hit 70fps vs. 58.6fps. Other titles, like Batman: Arkham City, Shogun 2, and Metro 2033 favored the GTX 660 by 50-70%. Then again, the cheapest GTX 660 is 1.43 times as expensive as the HD 7790.

Performance-wise, the HD 7790 is a clear improvement over the AMD HD 7770. Its overall value proposition, however, is less clear. AMD has set a baseline price of $149 for 1GB configurations?but HD 7850 2GB cards are available on NewEgg starting at $182. In this case, the extra $32 buys twice the RAM, 50% more memory bandwidth, and a higher pixel fill rate.

AMD intends to sweeten the deal by offering a free copy of Bioshock Infinite to new buyers as part of the Never Settle bundle, and that's a fairly enticing carrot. Asus's Direct CU dual-fan design keeps the HD 7790 running quietly, and there's some nice headroom in the GPU?we were able to increase the GPU clock to 1200MHz without touching the card's voltage and a modest voltage tap let the GPU hit 1275MHz while keeping temperatures below 65C.

The one fly in the ointment is how prices will settle out. If you've been eyeing an AMD HD 7770 at $100, but can afford to stretch a bit, the Asus Direct CU II Radeon HD 7790 is a nice deal at $150. If, on the other hand, you've been eyeing the $150 price point, the $185 AMD HD 7850 is still a better bet?$35 buys a hefty chunk of additional GPU power and the 2GB frame buffer is a nice bit of insulation against next-generation games with hungry VRAM requirements.

Source: http://feedproxy.google.com/~r/ziffdavis/pcmag/~3/2Xp3j023wl8/0,2817,2416921,00.asp

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