The ASUS HD6850 DirectCU comes pre-overclocked at 790MHz on the core. This is a rather tame overclock of 15MHz but the beauty of the ASUS card is its unique voltage tweak feature. No other cards on the market currently support this so ASUS have to be commended for their implementation. Teamed up with their DirectCU cooler, the HD6850 looked promising from the onset and the results did not disappoint in the slightest. At a stock speed of , the reference HD6850 is clocked quite conservatively given that the same Barts core comes at 900MHz on the HD6870 and the same rated memory chips are used. Nonetheless, it promises plenty of headroom thanks partly to a mature 40nm manufacturing process. To overclock the card, I used ASUS’s own Smart Doctor utility for voltage tweaking and increasing the clock speed. The process was very painless and soon a final clock speed of was reached using a voltage of 1.25V, 10MHz higher than what the HD6870 could achieve on stock voltage. For comparison, the HD6850 operates at 1.148V under load and when it idles, it operates at 0.945V clocked at . Unfortunately, Smart Doctor, MSI Afterburner and ATI Overdrive all limited the maximum core speed to 1000MHz, otherwise a higher result could have been achieved with an additional bump in voltage.






Looking at the benefits of overclocking, the 29% increase in core clock speed is mirrored by the same boost in texture fill rate, shader operation and pixel fill rate over reference specifications. Likewise, the 600MHz increase in memory speed results in a 15% boost in bandwidth. The card thus ends up being comparable to the HD6870, where the latter’s shader advantage is reflected in the higher operations.

In real world situations, the 29% core increase and 15% memory clock boost resulted in an average performance rise of 20%, not quite a linear trend but still a significant increase. This will become clearer from the following games’ benchmarks.

Temperature


The DirectCU may only have a 2 heat pipe design compared to the HD6870’s three, but from experience, it has proved to be a winner. So it made perfect sense for ASUS to use the cooler on the Barts core. At stock clock speed, the temperature delta is a mere 50C under load and 27C at idle, comparable to the results of the same cooler on the HD5850. The slightly higher temperature is down to the fan functioning at a lower speed, 24% at idle and 40% under load. The DirectCU cooler remains very quiet at those speeds.

When overclocked, the idle temperature rose to a delta value of 32C and a fan speed of 28%. Under full load, it did ramped up to 56% to keep the temperature delta at a stable 59C, cooler than any the other cards on test here. The fan became audible at 50% but wasn’t intrusive until it hit 60% or above.