Representing the first of the Northern Islands family of GPUs, Barts Pro and Barts XT (6850 and 6870, respectively) were adapted from the Cypress chips used in the HD 5800 series. As a stop-gap measure to tide us over until the 28nm Southern Islands GPUs come out in 2011, AMD intended to offer comparable performance to last year’s models while lowering price and power consumption. Though they used the same 40nm process, the transistor count was cut down from over 2 billion in the 5800s to about 1.7 billion in these optimized chips and clock speeds were increased substantially:
|AMD Radeon HD 6800 Series Specs|
|HD 6850||HD 6870|
|Core Clock||775 MHz||900 MHz|
|Compute performance||1.5 TFLOPs||2.0 TFLOPs|
|Texture Fillrate||37.2 Gtexel/s||50.4 GTexel/s|
|Pixel Fillrate||24.8 GPixel/s||28.8 GPixel/s|
|Z/Stencil||99.2 GSample/s||115.2 GSample/s|
|Memory Size/Type||1GB 256-bit GDDR5||1GB 256-bit GDDR5|
|Memory Clock||1,000 MHz||1,050 MHz|
|Memory Data Rate||4.0 Gbps||4.2 Gbps|
|Memory Bandwidth||128.0 GB/s||134.4 GB/s|
|Idle Board Power||19W||19W|
|Max Board Power||127W||151W|
Though basically cut from the same silicon, there are a few key differences that separate these two graphics cards. The increased core clock speed and stream processor count in the 6870 resulted in greater raw computing power than the 6850, for one. More texture units equates to a higher texture fillrate, etc. The only difference in memory is the 50 MHz between the two clocks, which separates them slightly by resulting bandwidth. There is also mild increase in maximum board power consumption, meaning the 6870 needs a second 6-pin power connector, as you’ll see on the next page.
Both appear to have significant advantages over the GTX 460, the most prominent being the much higher core clock speed and memory bandwidth. The latter is magnified in the case of the GTX 460 768MB, which has a narrower memory bus of 192-bit instead of 256-bit in the 1GB version and the Radeon 6800s. It is also worth noting that the 6800s are rated at lower TDPs than the 460s, at 127W and 151W compared to 150W and 160W.
Officially, the HD 6850 and 6870 are priced at $179 and $239, and there are several SKUs available now at your favorite e-tailer. This puts them right around the prices the GTX 460s launched at in July, albeit with a wider gap between the two.