ASUS GTX 660 DirectCU II TOP Reviewccokeman - September 13, 2012
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ASUS' GTX 660 DirectCU II TOP is the top card in its GTX 660 product stack. As a non-reference design the GTX 660 DirectCU II uses a custom PCB loaded with ASUS own specific technologies including the use of its Digi+VRM all digital power circuit featuring Super Alloy Power components including custom Chokes, MOSFETs, and capacitors. The GTX 660 comes in several flavors from ASUS to meet different performance and price targets. The TOP version that I am looking at has been through a rigorous testing and validation process that allows the card to run with a base clock of 1072MHz, boost clock speed on the core of 1137MHz or 104MHz above the reference GPU boost clock speed of 1033MHz. Each part of the card endures this testing and validation process to deliver long term reliability and stability. A first look of the card shows that the DirectCU II cooling solution is the most visible feature of the card. It employs a pair of 70mm "Dust Proof fans" to provide the up to 600% improvement in airflow over the reference design needed to keep the card cool and extend the life of the fans by up to 25%. That large increase in airflow allows the GTX 660 DirectCU II to run 78% cooler and 9dB quieter than the reference design. This card measures just 10.2 inches in length and is a two slot card with the DirectCU II cooling solution. Designed to be used in a 16x PCIe 3.0 expansion slot, the card is backwards compatible with PCIe 2.0 motherboards.
The back of the custom black PCB is mostly vacant with the exception of four of the mixed density GDDR5 modules seen surrounding the GPU socket. In the center of the socket area is part of the Digi+/SAP power package called the SAP cap. These capacitors store additional current right behind the GPU to provide that instantaneous boost of current needed to keep up with the current draw of a highly overclocked core improving stability under load. Looking at the top and bottom of the card the three 8mm "Direct Contact" nickel plated copper heat pipes that loop around and into the aluminum fin array are visible. The heat load is exhausted both into and out of the chassis but will not provide enough thermal dump into the chassis to overcome the vast majority of chassis airflow solutions. Aesthetically the GTX 660 mirrors the ROG inspired look of the rest of the DIrectCU II lineup. Putting the GTX 660 DirectCU II into any of ASUS' own ROG motherboards would be a perfect visual fit.
Connectivity on the GTX 660 DCU II consists of a single Dual Link DVI-I port, one Dual Link DVI-D, a single HDMI 1.4a port, and a single full-size DisplayPort 1.2 port. The maximum supported resolution is 2560x1600. Targeted for gaming with a resolution of 1920x1080, jumping to a triple screen surround setup will need a second card in SLI. However the GTX 660 can make use of another part of the NVIDIA ecosystem by using 3D Vision to deliver an additional dimension to your gaming experience. The back end of the GTX 660 DCU II has the shroud stopping at the end of the PCB with the PWM fan header on the bottom edge of the PCB.
Across the top of the PCB is a support brace used to keep the PCB from bending and cracking the trace routes in the PCB. A single SLI bridge connection is used to support just one other GTX 660 in an SLI configuration at this price/performance point. With a 140 watt TDP, a single 6-pin PCIe power connection is used. Starting the system up after a new build is a rush for most people. When everything powers up all is right in the world until you do not get a video feed. To combat this ASUS has incorporated its Protective Design feature set into this card with part of the feature set being the VGA LED. This feature gives the user a visual cue indicating whether they have power to the PCIe connection points on the card. Red means no power and to connect the power plugs, and green means all is well with the requisite 6-pin PCIe power connections in place. That bright red eye caught me in the rush to test this card.
ASUS' DirectCU II cooling solution is the most outwardly visible feature on this card. It utilizes three 8mm nickel plated copper heat pipes that flatten out as they travel through the contact surface to distribute the thermal load to the aluminum fin array. This aluminum fin array has five separate dissipation points and an optimized pitch design to most efficiently channel the load from the GPU to the airstream generated by the two 70mm dust proof fans. These fans use a dual seal to keep dust out of the hubs increasing the life span of the fans up to 10,000 hours over cards that do not use this fan technology. The GTX 660Ti DCU II TOP used a small extruded aluminum heat sink over the Digi+ VRM/SAP six phase power circuit but this card does not have one to help manage the reduced thermal load on the VRM circuit. The contact surface, much like most heat pipe direct contact designs, is smooth to the touch but not as smooth as a one piece contact plate. Even so the design is proven to be quite effective at transferring the thermal load from the GPU core to the aluminum fin array.
As another part of the ASUS Protective Design suite, the 70mm x 10mm fans use a dust proof design to extend the useful life span of the cooling fans by up to 25% over standard designs. These fans use two seals to reduce dust intrusion into the fan hub that can slow down the fans rotation over time. Using a non-sealed design would ultimately lead to compromising the cooling efficiency of the DirectCU II design. The eleven blade fans from First D deliver substantial airflow and higher static pressure through the shroud to improve cooling by up to 78% over a reference solution. Fan noise from video cards has been one of the necessary evils with air cooling over the years with reference blower designs being the worst offenders. ASUS' DirectCU II design as it is implemented on the GTX 660 DirectCU II TOP is dead silent from outside the chassis in normal operation running at 9dB quieter than the reference design. Spinning the fans up to maximum results in only a whir from inside the chassis to go along with the great cooling performance.
Stripping away the heat sink we can get a closer look at the PCB and take a look at the component layout. The VRM circuit on this card has been put on the back end of the PCB unlike the design used on the GTX 660Ti DirectCU II TOP. On the GTX 660 DirectCU II TOP, ASUS has used a six phase all digital power circuit using its Digi+VRM/Super Alloy Power package. ASUS' Super Alloy Power technology is meant to increase efficiency, extend component life, run cooler, and reduce electronic noise. Developing components that meet these needs was paramount to delivering a card that performs well and lasts for a long time without failure. The SAP chokes use special alloys and a concrete core to reduce the buzzing so commonly heard with less robust designs. The SAP Capacitors allow a 30% increase in the maximum voltage threshold all while increasing the lifespan by two and a half times over the reference card. The Super Alloy MOS is smaller, runs cooler, and handles up to 30% more current than traditional designs and is detailed in the slide below. At the back end of the PCB is the Digi+VRM digital controller used the control this feature set while delivering monitoring and software control of card via ASUS GPU Tweak utility.
NVIDIA is launching a new core with the launch of the GTX 660 rather than reuse GK 104. With this launch we get the full implementation of the 28nm, 2.54 Billion transistor GK106 core that is equipped with a total of three Graphics Processing Clusters, five SMX each equipped with 192 CUDA cores for a total of 960. Texture units come in at 80 with 24ROPs. The 2GB of GDDR5 memory is running through a 3 x 64-bit memory controller that supports mixed density memory. Clock speeds for ASUS GTX 660 DirectCU II TOP are significantly higher than the reference clocks at 1072MHz for the "base" clock and 1137MHz for the "GPU Boost" clock. Increases of 92MHz on the base and 104MHz higher on the boost clock than reference designs. That's not to say the clocks will not run higher when the power envelope is not exceeded. Instead of the capable Hynix memory modules seen on just about every enthusiast level card over the past year, ASUS has used Samsung GDDR5 part number K4G20325FD-FC03 that are specified to run at 1500MHz. Clock speeds on the installed GDDR5 memory are 1502MHz (6008MHz Effective) or just above the specified range of the memory.
On strictly a hardware level the GTX 660 DirectCU II TOP is going to run slower than the GTX 660Ti. Targeted at those 9800 GT users still not enjoying DirectX 11 or even first generation Fermi cards like the GTX 460s and last year's GTX 560Ti, the GTX 660 including ASUS GTX 660 DirectCU II TOP look to offer tremendous upside with just about the entire NVIDIA ecosystem including PhysX, 3DVision, and more.