ASUS GTX 660 DirectCU II Graphics Card Review

At last check, ASUS has four GTX 660 video card offerings to choose from. Three of them are their “TOP” factory overclocked versions, and the fourth is based on NVIDIA’s reference GPU core speed of 980 MHz (1033 MHz Boost Clock). Today’s review will be on the non TOP version, which carries a part number of GTX660-DC2-2GD5. While today’s sample might not be factory overclocked, it does still offer the same DirectCU II cooler and the same DIGI+VRM/Super Alloy Power designs. So, let’s run this card through its paces and find out if we have another worthy addition to the ASUS family of graphics cards!

Specifications and Features

Here are the specifications as provided by ASUS.

Much of what we see above can be verified using GPU-Z.

As I mentioned earlier, even though this card is not factory overclocked like the TOP versions, it still boasts many of the same features. We’ll dive deeper into the features as the review progresses, but here are the major ones listed on the ASUS website. The first set of features are described as “ASUS Exclusive Features”. I’m good with all that, except for the 2 Gb memory claim. I hardly think anything related to memory can be called exclusive, unless ASUS is making their own GDDR5. They don’t.

	DirectCU II DirectCU thermal design utilizes direct contact copper heatpipes so heat is dissipated efficiently, delivering a 20% cooler and vastly quieter performance than reference.
	DIGI+VRM with Super Alloy Power Acclaimed DIGI+ VRM has been applied via a power design that uses digital voltage regulators to minimize power noise by 30% and enhance power efficiency by 15%, widen the voltage modulation range, and improve overall stability and longevity by 2.5 times longer than reference.
	GPU Tweak Detailed specs and actual card status with GPU-Z Monitoring widget provides real-time and detailed multi-parameter info Automatically check and update drivers and BIOS versions
	Gigantic 2GB GDDR5 Memory On-board memory for the best gaming experience & the best resolution
	Windows 8 Ready Full support for Microsoft’s latest operating system, Windows 8 (x32 and x64). Also supports Windows 7, Vista, XP.

The next set of features are more related to NVIDIA cards in general. In case you are wondering, yes this card supports SLI.

Packaging and First Look

Not much has changed with the graphics applied to the box of ASUS DirectCU II video cards. They are still using the “claw marks” design on the front, along with some information on the cooler. The back of the box is where ASUS goes into much greater detail about the features. The box sides are designated for additional branding and mentioning of the DirectCU II cooler.

Box Claws… Errr Front
Box Left Side	Box Right Side
Box Top	Box Bottom
Box Back

Inside the outer box is an elegant looking black box with a gold ASUS logo on the top. Inside we find a folded cardboard insert with a clear plastic wrap securing the card to its environment. Just to the right side is another smaller box, which houses the only accessory included with the GTX 660 DirectCU II, a DVI to VGA adapter. Other than the adapter, you get the setup guide and CD that has the drivers and GPU Tweak software. As always, I recommend you check the ASUS website for the latest version of GPU Tweak and the NVIDIA website for the latest drivers.

Black Box
Card Secured in Box	Accessories

Photo Op

It’s hard to argue with the looks of any ASUS video card that has the DirectCU II cooler on it; but then again, I’ve always been partial to the black and red theme regardless of brand or component. Aesthetically speaking, if you already own an ASUS ROG motherboard, this card will be a seamless addition to your system. Before we zoom in for a closer look, enjoy the pictures!

Top View
Side View	Side Angle View
Side Angle View	Back Side
Back Side Angle View	Back Side Angle View

A Closer Look and Under the Hood

We’ll begin this section with a look at the power and display connectivity. This card uses a single 6-pin PCI-e power connection, which is located at the top rear area of the card. ASUS has also built in a red and green LED here to warn you if the 6-pin power lead is installed correctly and working properly. I’m sure you figured out green means all is good, and red means there is a problem.

6-pin PCI-e Power Connector

Green Means Go

For display connections, we have two DVI ports (DVI-I and DVI-D), one HDMI, and one DisplayPort; all of which are built on a dual slot bracket.

Display Connections

Connection Options Provided by ASUS

ASUS is proud of their DirectCU II coolers, and with good reason. There are innovative designs associated with the DirectCU II coolers that ASUS wants you to know about. The ASUS double-sealed, dust-proof fan design goes a long way towards the longevity of the video card and promises to extend the lifespan by up to 25% over traditional fan designs. The three heatpipes make direct contact with the GPU and provide a total of five dissipation points. Because of this design, ASUS claims a 125% larger dissipation area over standard cooling devices. That’s very believable. I couldn’t find the exact specifications of two the fans, but they are FirstD branded, and my trusty set of calipers tell me they are right at 80 mm in size. The model number of the fans suggest they might actually be 70 mm in size, but they do measure larger than that.

Thermal Design Provided By ASUS

Dust Proof Fan Design Provided By ASUS

Moving in for a closer look at the Direct CU II cooler, we find four spring loaded screws at the back of the card needing to be removed in order to separate it from the card. First off, we found a good application of TIM and one thermal pad. It appears the thermal pad was put there to cover just one of the memory chips. This is probably due to that particular memory chip not being located in a high air flow area. Adding the thermal pad to it allows the heat to be picked up by the heatpipes, instead of relying solely on air flow.

DirectCU II Removed
DirectCU II Removed	DirectCU II Removed

Four smaller screws need to be removed in order to separate the heatsink from the fan shroud. Looking closer at the fan shroud, we can see the before mentioned FirstD branded fans, along with the applied wiring technique.

Fan Shroud – Top Side

Fan Shroud – Back Side

Of the three heatpipes built into the DirectCU II, two of them are designed to pass through the coolers base and weave their way through the fin stack on both sides of the heatsink. The third heatpipe also goes through the base of the cooler, but only curves around to engage the larger side of the heatsink. This design makes perfect sense for distributing the heatpipes proportionally to the size of the heatsink. Other than the copper heatpipes, the entire heatsink is made of aluminum that ASUS has outfitted with their “Optimized Pitch” fin design.

Heatsink Removed from Shroud – Bottom Side	Heatsink Removed From Shroud – Top Side
Heatsink Side View	Heatsink Side View

Now that the GTX 660 DirectCU II is stripped, we can have a a closer look at the components on the bare card. The Digi+ VRM and Super Alloy Power designs are well known features to anyone familiar with ASUS video cards.

Power Deliver Features Provided By ASUS

Super Alloy Power Features Provided By ASUS

When compared to the NVIDIA reference card design, we can see that ASUS has really beefed up the power delivery section of the card. There is a six phase GPU PWM power delivery that uses a digital IC along with a three POSCAP design. This is a substantial increase from the reference design of four phase GPU PWM delivery with an analog IC, and only one POSCAP.

GPU PWM Power Delivery Provided By ASUS
GPU PWM Power Delivery Area	Power Delivery Side View

As you look at the above pictures, and the ones I’ll show below, take note of the chokes, PWM chips, and capacitors scattered about the PCB. These are not your standard fare components, and all of them are vastly improved from reference designs. The Super Alloy Chokes are different from standard chokes in that they are reinforced with a “special” alloy formula. This reinforcement process allows the chokes to run cooler than standard chokes, but best of all is the elimination of that annoying buzzing sound so prevalent in other video cards.

The Super Alloy Capacitors are said to offer a 2.5 times longer lifespan under normal operating conditions. Additionally, ASUS says they increase the voltage threshold by 30%. Sounds good to me.

The MOSFET area is decked out with the ASUS Super Alloy MOS design. This is a very impressive feature in that it manages to not only reduce the physical size of the chips, but also increases the voltage threshold by 30%. This MOSFET design is also said to run cooler and more efficiently than generic MOSFET designs.

SAP Chokes Explained By ASUS
SAP Capacitors Explained By ASUS	SAP MOSFETs Explained By ASUS
SAP Capacitors, SAP MOSFETS, and SAP Chokes	Full “Naked” PCB Shot
Another Choke and More Capacitors

Looking at the back of the GTX 660 DirectCU II and directly behind the GPU core, we find the SAP CAP feature. To better the transfer time of stored capacitance, ASUS locates this directly under the GPU. This feature greatly aids in efficient power delivery and promises greater overclocking potential.

SAP CAP Feature Provided By ASUS

SAP CAP Feature on Back

When compared to the reference design cards, the ASUS Digi+ VRM promises a 30% more stable overclock, 15% better power efficiency, and 50% less EMI. The Digi+ VRM is able to adjust voltages based on overclocking demands by way of digital settings that have been embedded into the chip.

In today’s world, power efficiency is something all manufacturers are trying to enhance. ASUS is doing their part with the Digi+ VRM requiring almost six watts less than the reference design. They are able to accomplish this by transferring current between phases and reducing power loss.

The Digi+ VRM is also said to reduce EMI by 50% through dynamic adjustment of electrical frequencies.

Digi+ VRM
Digi+ VRM Feature By ASUS
Digi+ VRM Efficiency By ASUS	Digi+ VRM EMI By ASUS

Samsung K4G20325FD-FC03 GDDR5 is the memory of choice on the GTX 660 DirectCU II. This GDDR5 memory is rated for 1502 MHz (6008 effective) and operates at 1.455 to 1.545 Vdd/Vddq.

Samsung GDDR5

The NVIDIA GTX 660 video cards have a new GK106 core, which attempts to fill the performance gap between the GK104 and GK107. The below chart will illustrate many of the differences between the GPU cores.

Meet the Kepler GK106

GK106 Angle Shot

To round out our look at the naked card, here are some additional images from various angles.

Bare Card Full View
Bare Card Angle View	Bare Card Angle View
Back of Card Angle View

Performance and Overclocking

Installed and Ready for Benching!

Test System

• ASUS Maximus V Formula Motherboard (Oveclockers Approved!)
• G.SKILL Trident X (2 x 8 GB) DDR3 2400 F3-2400C10D-16GTX @ 18666 MHz 9-9-9-24
• Kingston 3K SSD 240 GB (Overclockers Approved!)
• Intel i7 3770K Processor @ 4.0 GHz (Overclockers Approved!)
• Water Cooled/Swiftech Apogee HD CPU Block
• Corsair HX1050 PSU
• ASUS GTX 660 DirectCU II – 306.97 Driver

Benchmarking Methods

Since April of this year, we have been using our new “Updated Video Card Testing Procedure“. If you are not yet familiar with it, click the provided link to learn more. Below is the down and dirty version of the new procedure.

• All Synthetic benchmarks were at their default settings
• Unigine Heaven (HWbot) was run using the “extreme” setting
• Aliens vs. Predator – 1920×1080 with highest settings offered (4x AA, textures set to highest)
• Battlefield 3 – 1920×1080 at Ultra settings (4xAA/HBAO by default)
• Dirt 3 – 1920×1080 with 8x MSAA and all settings enabled and at Ultra where possible
• Metro 2033 – 1920×1080, DX11, Very High, 4x MSAA/ 16x AF, PhysX OFF, DOF enabled, Scene: Frontline
• Civilization V – 1920×1080, 8x MSAA, VSync OFF, High Detail Strategic View: Enabled, Other Settings: High, using full render frames value ( / 60)
• Batman: Arkham City – 1920×1080, VSync off, 8xMSAA, MVSS and HBAO, Tessellation set to high, Extreme Detail Level, PhysX Off

For comparison, we have cards ranging from the HD 7750 to a GTX 660 Ti. It’s been said that the GTX 660 cards should fall in between the AMD HD 7770 and HD 7850, in both performance and price.

Included Software

GPU Tweak is what ASUS provides for monitoring, overclocking, and fan control. GPU Tweak also includes an ASUS branded version of the popular GPU-Z utility. The monitoring portion gives you real time information on GPU temperatures, GPU usage percentage, GPU voltage, VID usage percentage, and a host of other values. For overclocking, the Tuning section of GPU Tweak is where you can adjust GPU Clock, memory clock, GPU voltage, and the power target percentage. The fan control options include Auto, Manual, and User Defined. Selecting User Defined allows you to customize fan speeds based on temperatures.

Overclocking for Stability

After opening GPU Tweak for the first time, the first thing that hit me was the power target slider that only offered +10%. This is by far the lowest available power target increase I have seen and will no doubt hinder overclocking. After some additional investigation, I found an article at HardOCP directly related to this. What they found out is once the TDP maximum has been breached through a combination of raising GPU voltage, GPU speed, memory speed, and even the fan speed, the GPU will be downclocked in order to keep TDP within the allowed limit of 150 Watts. This is not a situation caused by ASUS, but rather NVIDIA deciding they don’t want the TDP to be exceeded on the GK106 GPU. This limitation will hold true for any manufacturer that brings a GTX 660 to market. Even though I’ll still attempt to find the maximum stable GPU and memory speed, keep in mind this may not result in the best “real world” performance depending on how much over the maximum allowed TDP we end with.

To satisfy my own curiosity, I overclocked the video card and ran HWBot Heaven. I noticed fluctuation in the GPU core speed much like HardOCP reported. I outlined one of the fluctuation occurrences in the image below. You can use the GPU Tweak logging function to monitor the power target value, which will help you determine if you are breaching the power target wall.

Results of Breaching the TDP Limit

I was able to stabilize the card at a memory speed of 1663 MHz (6652 MHz effective) and a GPU Boost Clock speed of 1150 MHz. Below are the settings I used to achieve the overclock, along with the GPU-Z monitoring results. As you can see, while the card was under load, the Boost Clock speed was well above the 1150 MHz I had it set at. The Boost clock speed maxed out at 1201 MHz and would occasionally drop to 1188 MHz. The drop is more than likely due to the maximum TDP being breached, but even so it stayed well above where it was set at. The memory speed stayed consistent throughout the testing, never budging from the 1663 MHz it was set to.

Stable Overclock

Synthetic Benchmarks

As usual, our benchmarking session begins with our suite of synthetic tests. Beginning with 3DMark03, we find the HD 7850 and HD 7870 cards leading the way, followed by the GTX 660 Ti and our GTX 660. Because no one really optimizes for this older benchmark any longer, don’t put too much stock in these results other than perhaps the scaling when overclocked.

3DMark03 Results

Next up is the DX11 based 3DMark11. In this much more modern benchmark, we find a good showing by the GTX 660 DirectCU II. In its stock and overclocked condition, the ASUS GTX 660 beat all comers, except for the GTX 660 Ti. Good showing here.

3DMark11 Results

DX10 game titles are still widely utilized by many people, which still makes 3DMark Vantage a viable benchmark. We again see the ASUS GTX 660 beating the HD 7850 and HD 7870, at both stock and overclocked. It also wasn’t too far off the GTX 660 Ti.

3DMark Vantage Results

Our last synthetic benchmarks is HWBot Heaven. In a familiar theme, we see the ASUS GTX 660 DirectCU II besting all the competition, except for its bigger brother GTX 660 Ti. It’s pretty tough to complain about the synthetic benchmark results; let’s move on the the game benchmarks.

HWBot Heaven Results

Game Benchmarks

Our first game benchmark is Aliens vs. Predator DX11. The Sapphire HD 7870 managed to beat out our review sample here, but just barely. When the GTX 660 was overclocked, it held tight to the GTX 660 Ti.

Aliens vs. Predator results

Continuing on in alphabetical order, we land at the Batman: Arkham City benchmark. Here we find the ASUS GTX 660 with scores almost identical to the GTX 660 Ti. This result is pretty impressive given that the GTX 660 Ti is one of the ASUS TOP cards, meaning it’s factory overclocked.

Batman: Arkham City Results

Our Battlefied 3 results show another win over the HD 7850 and HD 7870 AMD cards. The GTX 660 fell a little farther behind the GTX 660 Ti here, but was still competitive.

Battlefield 3 Results

In Civilization V, we again find an excellent result for our review sample. The ASUS GTX 660 nipped at the heels of the GTX 660 Ti and came within a fraction of overtaking it when the overclocked results were compared. Both the HD 7850 and HD 7870 fell substantially behind here as well.

Civilization V Results

The ASUS GTX 660 DirectCU II continued to show impressive numbers during the Dirt 3 benchmark. We still show dominance over the HD 7850 and HD 7870, and continued a good showing against the more powerful GTX 660 Ti.

Dirt 3 Results

Our last game benchmark is the GPU crushing Metro 2033. None of the cards in the graph achieved the 30 FPS we consider a playable frame rate. There is little difference between the higher end AMD and NVIDIA cards in our comparison chart, but another good showing for the ASUS GTX 660 DirectCU II none the less.

Metro 2033 Results

Cooling and Power Consumption

Overclockers’ temperature testing procedure requires running HWBot Heaven at both stock and overclocked settings. The results are normalized to 25° C ambient and the fan settings are set to automatic (default). The DirectCU II cooler did a great job of keeping things cooled off at both stock and while overclocked. Not only does the DiretCU II cooler do a great job of keeping the card cool, it does so with very little noise. During the temperature testing, the fan ramped up as the load on the card increased, but always remained very quiet. Great cooling and low noise; nothing to complain about here.

Cooling Test Results

Our power consumption testing is done with a Kill-a-Watt and wattage usage recorded at idle and load. We run both HWBot Heaven and 3DMark 11 (Combined Physics Test) to hopefully get the maximum power draw the video card can produce. I tend to take this testing one step further and also provide results while the video card is overclocked.

Power consumption again showed good results for the ASUS GTX 660 DirectCU II. There isn’t going to be a large difference between stock and overclocked results here, mainly because of the TDP limit NVIDIA has applied to the GK106 GPU.

Power Consumption Results

Excellent cooling and easy on your electric bill. Again, nothing to complain about here.

Pushing the Limits

There wasn’t a whole lot left in the card past what I had already accomplished in the “overclocking for stability” section. I was able to get 3DMark03 to finish with the GPU set to 1170 MHz and the memory set to 1675 MHz (6700 effective). This resulted in just short of 4000 in score increase, not too shabby there!

3DMark03 Pushing the Limits

Keeping the same settings as above, I went for a run of HWBot Heaven. The end result was an increase in score of about 20.

HWBot Heaven Pushing the Limits

We’ll finish up the Pushing the Limits section with a run of 3DMark11 at the same settings. Here, we see a little more than 200 in score increase. Nothing to sneeze at there either!

3DMark11 Pushing the Limits

Conclusion

Even with NVIDIA’s attempt to throttle this GK106 GPU through capping the power target, I think ASUS did a great job with what they had to work with. The card still overclocked quite well, which is a tribute to the ASUS Digi+ VRM, Super Alloy Power, and beefed up power phase designs. It pretty much dominated the AMD HD 7850 and HD 7870 in almost all of our testing, especially the game benchmarks.

The price on the ASUS GTX 660 DirectCU II is $234.99 at Newegg, which puts it right in line with HD 7870 pricing. Some HD 7870 cards are priced about $10 less, but many are priced higher as well.

The DirectCU II cooler always seems to to a great job, regardless of what model video card ASUS puts it on. It really is one of the best brand specific coolers out there. Even under the most demanding overclocked conditions, the card never even sniffed dangerous temperatures.

The bundled GPU Tweak utility is a great companion when trying to push your video card to its limits. Best of all, it just plain works from top to bottom.

So, what we have here is a good performing video card that’s priced right, overclocks quite well, and has many onboard components not found on many competitor offerings. All told, the ASUS GTX 660 DirectCU II is definitely worth considering if the price and performance levels are equal to your interests.

Click the stamp for an explanation of what this means

-Dino DeCesari (Lvcoyote)