APU, Motherboard and Memory
We already covered the technical details of AMD’s Kaveri architecture in our launch story, AMD A10-7850K and A8-7600: Kaveri Gives Us a Taste Of HSA, so we'll just review the high-level points.
Kaveri’s x86 CPU cores are based on the Steamroller architecture, AMD’s most modern design, while the graphics engine employs Graphics Core Next, also a first for APUs. In addition, AMD revamped its Heterogeneous System Architecture to facilitate improved developer access to the platform's resources.
These APUs are manufactured on a 28 nm process at GlobalFoundries, and sport better efficiency than the Llano, Trinity, and Richland APUs preceding them. So far, so good.
Like the A10-7850K, the -7800 features a capable graphics unit with 512 GCN-based shaders. This newer model sports slightly slower base and Turbo Core clock rates, and doesn't include an unlocked multiplier.
This APU is highly complex. The 245 mm2 die hosts a whopping 2.41 billion transistors. But even though this is a fairly complete SoC, Kaveri requires a number of other platform components still.
We Need RAM, Fast RAM
It's not news that AMD's host and graphics processing subsystems benefit from fast system memory. The processor’s integrated memory controller supports DDR3-2133, and for our experiment, we went with AMD-branded memory rated for up to DDR3-2400. While we didn’t experience stability issues at 2400 MT/s, the performance increase over DDR3-2133 was marginal. Feel free to stick with the lower data rate and tighter timings.
A Simple Taste In Motherboards
Our German team is cycling through three different motherboards for APU testing, depending on form factor and focus. However, after extensive measurements, MSI's A88XM Gaming emerged as the most efficient. None of the APUs experienced stability issues with it, and its BIOS allows us to conveniently set underclocking and overclocking options to optimize the thermal ceiling.
A maximum of 8.2 W can be attributed to the motherboard under full load, which includes 16 GB of overclocked DDR3-2400 RAM. At idle, its power consumption drops to approximately 5 W. Needless to say, those values do not include the APU itself. Unsurprisingly, the motherboard derives the DIMMs’ supply voltage from the 12 V rails of the 24-pin connector.