Articles: Graphics

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PCB Design

The graphics card we are testing today resembles Sapphire’s Radeon HD 6970 2GB Dual Fan which has the same cooler. Probably to avoid confusion, Sapphire wrote this card's model name right on the plastic casing.

The sculpted casing has acquired two chrome inserts at the sides of the fans. The card is 275 millimeters long. Its height and width are 100 and 42 millimeters, respectively.

Like the reference AMD Radeon HD 7950, the Sapphire Radeon HD 7950 OC offers one dual-link DVI-I port, one HDMI 1.4a connector and two DisplayPorts version 1.2.

This cooler doesn’t really need a large vent grid in the card’s mounting bracket, but Sapphire didn’t install a second DVI-I connector at the expense of the grid. This is not a big problem considering the included adapter, though.

The power and MIO connectors and the dual BIOS are all the same as on the reference Radeon HD 7950.


We can see two 6-pin power connectors, two MIO connectors for CrossFireX configurations and a switch for choosing the BIOS to use. The peak power consumption of the Radeon HD 7950 in 3D mode is declared to be 200 watts. It is going to lower to 70 watts in 2D mode and to 3 watts when the monitor is turned off. Considering the pre-overclocked GPU frequency, the Sapphire card is going to need somewhat more power than the reference sample, but not by much.

Two BIOSes are available with the Sapphire Radeon HD 7950 OC 3GB. One has more aggressive fan settings so that the cooler could handle the GPU and power components more effectively at increased frequencies and voltages.

With all of the cooler’s elements removed, the card looks like that:

The power system consists of six phases for the GPU and 2+1 phases for the memory chips and voltage converter.


In fact, the Radeon HD 7950 has the same power circuit as the HD 7970 but lacks high-quality DirectFETs. It employs the same controller CHiL CHL8228G, though.

The 28nm Tahiti Pro chip lacks any marking:

It has a standard Radeon HD 7970 configuration with 1792 unified shader processors, 32 raster back-ends and 112 texture-mapping units. The Sapphire Radeon HD 7950 OC has a GPU clock rate of 900 MHz at 0.993 volts in 3D mode. The frequency is lowered to 300 MHz at 0.850 volts in 2D mode. Thus, Sapphire’s factory overclocking amounts to a hefty 100 MHz here.

Like its senior cousin, the Radeon HD 7950 is equipped with 3 gigabytes of GDDR5 memory in 12 FCFBGA-packaged chips located on the face side of the PCB and manufactured by Hynix Semiconductor. They are labeled as H5GQ2H24MFR T2C.

The rated clock rate of such chips is 5500 MHz in 3D mode but, like the reference Radeon HD 7950, the Sapphire clocks its memory at 5000 MHz with a voltage of 1.6 volts. It's a shame since the chips do have tremendous potential as you will see shortly. The memory bus is 384 bits wide, providing a bandwidth of 240 GB/s. The card drops its memory frequency to 600 MHz in 2D mode.

Using GPU-Z, we determined the “quality level” of the GPU of our sample of the card. It is not very high at 76.1%.

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