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Review: AMD Radeon HD 7850 & 7870
by Damien Triolet
Published on March 13, 2012

Specifications

The raw figures for the Radeon HD 7800s are slightly down on those for the Radeon HD 6900s. Just as the Radeon HD 7870 can be seen as a double Radeon HD 7770, the Radeon HD 7850 is a double Radeon HD 7750, though with a slightly higher GPU clock. The gap between the two Radeon HD 7800s is however very high, as with the Radeon HD 7700s: 45% compared to 20% between the Radeon HD 6900s!

For this test, AMD supplied us with a reference Radeon HD 7870 and 7850:

The reference Radeon HD 7870



The reference PCB on the Radeon HD 7870 measures 24cm long, but the cooling system casing sticks out by more or less 1cm. This cooler uses a radial fan, or blower, to expel hot air out of the casing. It's made up of a copper base from which 3 heatpipes lead up to an aluminium radiator. This cooling block is surrounded by a cage formed by a casing and a metallic plate that supports the block and is in contact with the memory modules. It isn’t however in contact with the sensitive power stage components but there is an opening to allow them to benefit from part of the air flow.

To power the GPU (TDP = 190W) the power stage has 5 relatively basic phases which are situated between the GPU and the bracket rather than at the back of the card. There's an additional phase for the Hynix GDDR5 T2C memory that’s certified at 1.25 GHz. Two 6-pin power supply connectors are required.

The connectivity is identical to that on the other reference Radeon HD 7000s: a DVI Dual Link, a 3 GHz HDMI 1.4a out and two mini-DisplayPort 1.2 outs. There’s just one CrossFire connector, limiting the Radeon HD 7870 to a bi-GPU set-up.

When it came to overclocking, we managed to modify the GPU voltage to obtain the following (GPU clock / memory clock @ GPU voltage: energy consumption of the card in Anno 2070):

1000 / 1200 MHz @ 1.050V: 94W
1000 / 1200 MHz @ 1.219V: 124W (by default)
1175 / 1500 MHz @ 1.219V: 144W
1200 / 1500 MHz @ 1.250V
1225 / 1500 MHz @ 1.275V
1250 / 1500 MHz @ 1.300V: 177W


The reference Radeon HD 7850



The reference Radeon HD 7850 is identical to the Radeon HD 7870 described above, with one exception: its power stage uses just 4 of the possible 5 phases for a lower TDP of 150W.

With the tools currently available, we weren’t able to change the GPU voltage (GPU clock / memory clock @ GPU voltage: energy consumption of the card in Anno 2070):

860 / 1200 MHz @ 1.213V: 103W (by default)
1000 / 1550 MHz @ 1.213V: 119W

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