What’s the real benefit of six cores versus five, four, three, two, or one? This article looks at the performance, power, and efficiency of AMD's Thuban-based six-core Phenom II X6 1090T processor running with several different core configurations.
For more back-story on 890FX and the Phenom II X6, check out our launch coverage: AMD Phenom II X6 and 890FX Platform Review. It contains all of the details on AMD’s latest flagship offering. In this, we also mentioned how to unlock the Zosma quad-core into a Thuban six-core, though AMD has since announced that the quad-core Zosma probably won't make it to retail any time soon.
AMD has two different Thuban versions: the Phenom II X6 1090T at 3.2 GHz and the 1055T at 2.8 GHz. Both are based on a six-core design that offers 512KB L2 cache per core and a shared 6MB L3 cache. A crossbar switch enables access to the dual-channel DDR3 memory controller and the HyperTransport link connecting the CPU to the chipset.
All new four- and six-core processors (Zosma and Thuban) implement AMD’s Turbo CORE feature, which dynamically accelerates the processor to clock speeds beyond the nominal speed. The amount of acceleration depends on system load, and it does not automatically slow down unused cores. Still, the feature gives you an extra few hundred megahertz during peak load situations so long as the thermal envelope allows.
Switching individual cores off means there should be more thermal headroom for taking frequent advantage of the Turbo CORE feature. Benefits should be visible in applications that weren’t optimized to take advantage of multiple processing units. In these cases, the dynamic acceleration feature should accelerate one or two cores to maximum speed. Unfortunately, this isn’t reflected in our benchmark results.
Motherboards
While technically all Socket AM3 motherboards are capable of running processors on fewer cores, we wanted to use a solution based on the latest 890FX chipset. So far, we've only compared a few 890GX motherboards with integrated graphics (Ed.: since this piece was written, we've also published a five-board 890FX motherboard roundup, too). So, we decided to use the Asus Crosshair IV Formula again.
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It remains to be seen how many Socket AM3 motherboards are equipped with the necessary BIOS functions to disable individual processing cores. Based on our observations of Intel’s LGA 1366-based options, there are very few board/BIOS combos on the market that allow switching your CPUs to use an individual core count.
We used Asus’s 890FX Crosshair IV Formula board, which allows setting an individual number of active CPU cores.
