AMD Radeon HD 6850 and HD 6870 1GB
We published a special report about the new graphics cards titled ATI Radeon HD 6800: Generation Next. So in this section we will just give you some more info on the reference Radeon HD 6850 and Radeon HD 6870 models (on the left and on the right, respectively, in this and other photographs):
So, the Radeon HD 6850 is 229 millimeters long and its cooling system doesn’t exceed the dimensions of the PCB. The card’s height is 36 millimeters. The GPU is placed closer to the mounting bracket, the distance from the closest mounting hole of the GPU heatsink to that bracket being 74 millimeters, which makes it impossible to install many alternative coolers.
The Radeon HD 6870 is 242 millimeters long, i.e. 13 millimeters longer than its cousin. Its cooler protrudes beyond the PCB by 7 millimeters. The height is the same 36 millimeters. The GPU is placed closer to the mounting bracket, too, but the distance from its heatsink to the bracket is 87 millimeters (more than on the HD 6850). The diagonal distance between the GPU heatsink's mounting holes is 75 millimeters on both cards, just like on the Radeon HD 5870 and 5850.
The graphics dies of the Radeon HD 6870 and 6850 are the same size of 255 sq. millimeters. They only differ with their markings and manufacturing dates: weeks 37 and 36 of 2010 for our 6850 and 6870 samples, respectively.
We can remind you that the Radeon HD 6850's GPU has 160 unified shader processors and 8 texture-mapping units less than the HD 6870. Its frequency is 775 MHz as opposed to the HD 6870's 900 MHz. Both cards drop their GPU frequency to 100 MHz in power-saving mode. The GPU voltage is also lowered then: from 1.094 V to 0.95 V on the HD 6850 and from 1.172 V to 0.95 V on the HD 6870.
Each card is equipped with 1024 megabytes of GDDR5 memory from Hynix Semiconductor Inc. These H5GQ1H24AFR T2C chips have a rated voltage of 1.5 volts and a rated frequency of 5000 MHz.
All of the chips are placed on the face side of the PCBs. The memory bus is 256 bits wide. The Radeon HD 6850 has a memory frequency of 4000 MHz and the Radeon HD 6870, 4200 MHz.
Here are the parameters of the reference cards:
These cards have completely different coolers:
The GPUs are cooled with small aluminum heatsinks with copper soles. The difference is that the Radeon HD 6850 has an evaporation chamber in the base of the heatsink while the Radeon HD 6870 has a copper plate with grooves for three heat pipes. Two of those pipes are 6 millimeters in diameter and the central one is 8 millimeters.
The blowers of these cards differ in shape (the Radeon HD 6870 has a wider blower) as well as in electrical parameters. The Radeon HD 6850 has an 8.4W FirstD fan (marked as FD9238M12D). The Radeon HD 6870 is equipped with an FD9238Р12S fan from NTK Ltd.
The speed of the fans is regulated automatically through pulse-width modulation. By the way, the former card’s fan is fastened in the cooler’s plastic casing while the latter’s one is secured on a metallic frame. This difference couldn’t but affect the noise level which we will discuss later on. Right now, let’s check out how hot these reference graphics cards are.
Here is how we tested the coolers of these and other cards. We install the graphics card into a closed system case whose configuration is listed in the next part of the review. The ambient temperature is constant at 24°C. The system runs FurMark version 1.8.2 launched from a renamed EXE file at 2560x1600 with 16x anisotropic filtering forced on in the driver. We use GPU-Z 0.4.7 and MSI Afterburner 2.0.1 beta 1/2/3 for monitoring. The test is performed before we take off the graphics card’s cooler and with its default GPU thermal interface.
Here are the results of the two first cards in the automatic fan control mode…
...and at the highest fan speed.
So, the graphics core of the Radeon HD 6850 is as hot as 93°C in the automatic mode while its power components are 74°C hot. The fan speed grew from 1000 to 2435 RPM at that. Despite its higher frequency, the GPU of the Radeon HD 6870 is no hotter than 87°C and the power components not hotter than 82°C at 2430 RPM. The difference in performance between the reference coolers of the Radeon HD 6850 and 6870 is obvious at the maximum fan speed where the Barts Pro is as hot as 78°C and higher even at 4000 RPM whereas the Barts XT is only 62°C hot at 4420 RPM. Well, as a matter of fact, each blower is uncomfortably noisy even at 1900 RPM and downright loud at 2400 RPM and higher.
When in CrossFireX mode, both pairs of graphics cards have even higher temperatures and fan speeds.
Considering the revised PCB layout (the GPUs are now closer to the video interfaces), installing alternative coolers on these graphics cards is problematic. For example, the new Thermalright Shaman can be installed neither on the reference Radeon HD 6850 nor on the reference Radeon HD 6870. The high-performance cooler Accelero XTREME 5870 from Arctic Cooling doesn’t fit on the Radeon HD 6850 but suits the Radeon HD 6870 nicely.
But you can see that some 50 millimeters of the cooler’s length are redundant. So, you can limit yourself to the Arctic Cooling Twin Turbo Pro, especially as it has already acquired official support for the new Radeon series products. When used with an Accelero XTREME 5870, the Radeon HD 6870 became very cool even without heatsinks on its power components and at a quiet speed (1100 RPM) of the three 92mm fans.
At the maximum speed of the three fans, the GPU temperature is only as high as 57°C.
When we tried to overclock our cards, the two samples of Radeon HD 6850 achieved similar GPU frequencies (890 and 910 MHz) without losing their stability or image quality. We didn’t try to overclock them with a voltage increase because we couldn’t provide good enough cooling for them. As for the graphics memory, one sample stopped at a modest 4520 MHz while the other achieved a peak memory frequency of 4880 MHz. The overclocking results of the better sample are shown in the next screenshot:
The two Radeon HD 6870 samples with reference coolers and with default GPU voltages overclocked differently: one sample achieved a higher GPU frequency and the other sample, a higher memory frequency.