HD3870X2, more details



You may have noticed from previous pages that the HIS and Jetway HD3870 X2 VGA cards look very familiar. Well, you have not been fooled, both cards are based on the same AMD reference design and are all manufactured at the same location. We laid both review samples side by side, the only difference is the sticker found on the DC cooling fan, nothing else. As far as specifications go, there is again no difference:



Compared to the standard HD3870, the X2 clocks the GPU 50 MHz higher but the memory clock has been reduced by 225MHz (DDR). Because of the design of the video card, the system bus speed is not PCIe 2.0 compatible as first stated but instead PCI Express 1 with 16x lanes. All together we think that the HD3870 X2 will perform on par with the dual VGA CrossFire setup existing out of the single GPU HD3870's.

From a closer viewpoint you may spot few of the usual HD3870 options, for example the dual DVI-I connections and video out. Via a HDMI dongle this product is complete HDCP compatible and can produce sound and image, as well as transport those to a HDMI compatible display.

The X2, which indicates double HD3870 technology, comes with only one CrossFire interface, this is still sufficient to build a gaming setup existing out of four RV670 cores, i.e. Quad CrossFire. CrossFire X, which allows three or four GPU's to co-operate, is supported since latest Catalyst version 8.3.

Underneath the heatsink you'll find a PCB which is completely stacked full of electronics:



The HD3870 X2 is based upon the AMD RV680 chipset, in reality this is nothing but dual RV670 GPU’s connected with each other via a PCI Express bridge chip. The chip has 48 PCIe lanes, 16x for each GPU and the remaining 16 are being used for the system interface. This is why the HD3870 is not PCIe 2.0 compatible; the bridge chip doesn't support it. The following picture explains it pretty well how the dual GPU video card can produce CrossFire performance:


Image courtesy of PLX Technology

PEX8547 PCIe 16x bridge chip	RV670 core, you get two of those

As you may know, the 55nm RV670 core does produce quite some heat and with two of those processor placed onto the same board it is far from simple to prevent the device from overheating. The X2 is equipped with two independent heatsinks per core, airflow is created by a rotary DC fan which is temperature controlled to reduce the sound level whenever the system is 'idle'. Heated air is guided through the heatsink and exhausted out of the pc housing via the PCI bracket ventilation holes. This, of course, will make the second GPU quite a bit warmer because it uses air that is all ready warmed up by the first GPU. To improve cooling ability the second GPU heatsink is made out of copper, in long stress periods copper does perform better then aluminum, the downside is that the costs may increase quite a bit because copper if far from cheap these days.

The bridge chip and memory chips also have their own heatsink: overall the X2 weighs quite a lot just because of all the cooling that is required on this card. Notice the warning symbol on the heatsink which indicates that you better not touch the video card during operation.



Both GPU heatsinks have their own mountain bracket, all-in-all removing the complete heatsink isn’t that hard but it requires some patience because of the high amount of screws you have to remove. The back side of the PCB is passively cooled, half of the memory chips are located on this side of the video card.

The HD3870X2 is equipped with 1GB graphics memory. We found Samsung K4J52324QE-BJ1A chips on our samples, these are GDDR3 memory chips rated for up to 1000MHz. AMD clocked them at only 900MHz, this way you should have quite some overclocking headroom.

All this together you can expect quite high power consumption, AMD equipped the X2 with a 6-pin and a 8-pin PCIe power connector, although using two 6-pin PCIe connectors is good enough to enjoy full performance with overclocking options enabled.



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