AMD Radeon R9 285 Review: Tonga and GCN Update 3.0

Test Setup and Benchmark Suite

Power Consumption Measurement Methodology

Tom’s Hardware Germany’s test system for the exact measurement of graphics cards’, CPUs’, and other components’ power consumption was developed in cooperation with HAMEG (Rohde & Schwarz). It was designed for particularly precise measurements with very small time intervals and has a temporal resolution of up to 1 ms.

Only sophisticated technology is able to handle the challenges presented by AMD’s PowerTune and Nvidia’s Boost technologies. These generate changes in core voltage in time frames of under 10 ms, which results in very large and quick voltage fluctuations. Let’s take a look at what can happen in the space of only one single millisecond, using measurement intervals of 10 μs.

This is why we’re evaluating all measured currents and voltages with a 500 MHz four-channel oscilloscope with a data logger, the HAMEG HMO3054, and extremely fast current probes. This setup also allows for unified data storage and remote control.

The measurements provided by the three high-resolution DC current probes, all HAMEG HZO50s, are taken via a riser card for the 3.3 V and 12 V rails, which we constructed specifically for this purpose. It supports PCIe 3.0 and uses short signal paths. The remaining probes are connected to the PCIe power cable that we modified for this.

We measure the voltages directly at their respective rails. We’re now working with a temporal resolution of 1 ms, since this allows us to record and evaluate the fluctuations caused by AMD’s PowerTune and Nvidia’s Boost technologies with confidence.

We’ve limited the measurement duration to 1 minute due to the very high volume of data when we measure all channels. We only shorten the measurement intervals all the way to the minimum that the physical capabilities of our setup allows for our more detailed measurements.

Benchmarking Hardware And Software

The Radeon R9 285 was tested with the 14.8 beta launch driver, but all other AMD cards were outfitted with the Catalyst 14.7 RC1 for testing. The GeForce cards used the newest option, which at the time of testing was the  340.52 WHQL driver.

We selected a variety of newer game titles with high detail settings at a resolution of 1920x1080 in order to give the Radeon R9 285 and its competitors a solid, real-world workload that this class of card should be able to handle.

The Asus Radeon R9 285's core clock was dropped to the 918 MHz reference specification in order to show what a typical Radeon R9 285 should be able to accomplish. Keep in mind that there is no reference cooler for this card, so all Radeon R9 285 will be unique in this respect.

Some readers will note that the Radeon R9 280 results are those we collected from our Sapphire Dual-X Radeon R9 280 review.  Sapphire's card comes with a 940 MHz core clock, a mere 7 MHz over the reference specification. We took a few benchmarks with the reference clock but quickly realized that the results are within the margin of error, so we're using the Sapphire numbers to represent reference Radeon R9 280 results. Keep in mind that there is no reference Radeon R9 280 cooler, either.

Two of the games we're testing have an option to use a Mantle code path, so we're running those benchmarks (Thief and Battlefield 4) with Mantle enabled and disabled to measure the API's impact.

Graphics cards like the Radeon R9 280 require a substantial amount of power, so XFX sent us its PRO850W 80 PLUS Bronze-certified power supply. This modular PSU employs a single +12 V rail rated for 70 A. XFX claims continuous (not peak) output of up to 850 W at 50 degrees Celsius.

We've almost exclusively eliminated mechanical disks in the lab, preferring solid-state storage for alleviating I/O-related bottlenecks. Samsung sent all of our labs 256 GB 840 Pros, so we standardize on these exceptional SSDs.