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Closer Look at AMD Radeon HD 7870 GHz Edition and HD 7850 Graphics Cards

PCB Design

The reference Radeon HD 7870 GHz Edition and HD 7850 resemble top-end Tahiti-based products with their glossy black casing that has an eye-catching red insert in the center.

 

The cards are 252 millimeters long, which is 26 millimeters shorter than the reference HD 79xx. They are the same height (38 millimeters) and width (100 millimeters), though.

The reverse side of the PCB is open:

 

We can see power connectors and one MIO connector for CrossFireX configurations:

 

Each card has the same selection of video interfaces: one dual-link DVI-I, one HDMI and two mini-DisplayPorts. There is also a vent grid in the mounting bracket for exhausting the hot air out of the system case.

The cards differing in their power consumption and heat dissipation, the Radeon HD 7870 comes with two 6-pin power connectors while the Radeon HD 7850 has only one such connector.

  

Each card has only one CrossFireX connector:

The PCBs of the new cards resemble the reference Radeon HD 6870 and do not differ much from each other.

 

The power system is located between the video outputs and the GPU. It is 5+1+1 phases (GPU+memory+PLL) on the Radeon HD 7870. The HD 7850 has only 4 GPU power phases.

 

The power system is managed by a CHiL Semiconductor CHL8225 controller:

The Pitcairn XT and Pro chips of our cards are almost the same age. The HD 7870’s GPU was manufactured on the 52nd week of 2011 while the HD 7850’s on the 51st week of 2011.

 

You can refer to the previous section of this review for details on the GPU specs.

Each card is equipped with eight FCBGA-packaged chips of GDDR5 manufactured by Hynix Semiconductor. Labeled H5GQ2H24MFR T2C, they have a total capacity of 2 gigabytes.

Each card has the same memory clock rate of 4800 MHz in 3D mode. It is lowered to 600 MHz in 2D mode. The memory bus is 256 bits wide.

The latest version of GPU-Z reports that our GPUs have a rather low quality level: 68.8% for the HD 7870 and 65.7% for the HD 7850.

 

 
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