HIS HD6990 4GB Graphics Card Review

👤by Sahil Mannick Comments 📅17-06-11
Closer Look (Continued)

AMD HD6990 VS HD6950

With the two cards sitting next to each other, the size difference between the single and dual GPU cards is apparent. At 30.5cm, the HD6990 is 3.1cm longer than the reference HD6970/6950. In terms of styling, both follow the same shroud design. The fans are positioned differently with the HD6990 sporting a slightly bigger one.

Nvidia GTX590 VS AMD HD6990

The HD6990 is also longer than Nvidia’s dual GPU alternative by 2.2cm. It is also clear that the fan on the Nvidia card is larger in diameter and a down-draft rather than the blower type on the HD6990.

Removing the back plate

Removing the back plate reveals the network of circuitry that dominates the PCB. None of the PCB real estate has gone to waste in AMD’s attempt at creating a stable and efficient graphics card. There are a total of 8 256MB memory modules on the rear split into two groups on either side of the board pertaining to the two separate GPUs. Unlike the GTX590, there is symmetry in the board design. Thermal pads on the back plate provide additional cooling to the memory modules.

The shroud and cooler

Removing the shroud reveals the fin based blower fan placed between two large vapour chamber coolers for each heatsink. The fan uses a standard 4 pin PWM adapter. A metal bracket holds both heatsinks and provides additional cooling to the PCB components. In fact, the bracket has a distinct grill shape in the middle to maximise dissipation surface area.

The vapour chamber cooler

Both GPUs are independently cooled by a 37 aluminium finned heatsink that dissipate heat from the underlying vapour chamber. The copper heat plate contains liquid in the base (the raised middle part of the plate that is in contact with the GPU). The liquid evaporates and absorbs further latent heat through its phase transition to vapour. This rises and condenses on the outside upper part of the heat plate releasing heat which is then transmitted to the overlying fin array whilst the condenser fluid circulates around the outside of the heat plate. These types of coolers have proved very efficient in the past so we expect more of the same on the HD6990.

The base of the cooler

The underside of the cooler and shroud uses a metallic construction and sports more thermal pads to cool the rest of the memory modules. An additional thermal pad cools the ATI CrossFire bridge chip. We also see that the base of the vapour chamber coolers is copper for more efficient heat transfer.

Closer look at the fan

The fan looks very simple in design but we are confident that AMD know what they are doing. The circular ring above the fins prevents vibrations and a more stable fan.

The bare PCB

Finally, we have the PCB itself. The design has rotational symmetry which helps manufacturing costs and ensures same length traces from the VRM circuitry to each core. The ATI CrossFire chip is off centre to make way for the power regulators.

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