Lab Tested: AMD's Bulldozer Packs Plenty Of Cores, But Not Enough Power

Earlier this year Intel made waves with its Sandy Bridge processors, which served up impressive performance gains over their predecessors while improving energy efficiency. AMD’s return salvo is finally here in the form of the AMD FX platform, previously codenamed Bulldozer.

AMD built the FX platform with multi-threaded software in mind, juggling speed and power consumption to deliver strong, energy-efficient performance for the growing list of applications built to take advantage of multi-core processors. To that end, the Bulldozer platform supports up to eight physical cores.

That’s… a lot of cores. It's a number usually reserved for server hardware--a conclusion I found myself coming back to fairly often while putting the platform through its paces. And while the Bulldozer platform is a significant step forward for AMD, it fails to outshine the potent competition.

Inside the FX Platform

AMD built a fair amount of new technology into the Bulldozer architecture, along withquite a few refinements. AMD’s Turbo Core makes an appearance as well.

Here's how Turbo Core works: processors have heat and power thresholds, beyond which their stability becomes compromised. We call this limit their thermal design power (or TDP). When a CPU hasn’t hit its limits while it’s running, there’s inevitably bit of room left to push it's frequency up, automatically overclocking it. Intel's variant of the same process came first -- they call theirs Turbo Boost.

With Bulldozer, Turbo Core gets a bit smarter. If an app is using some, but not all, of the available processor cores, Max Turbo increase the clock speed on the cores that are in use. If an application is taking advantage of every single core, Core Turbo will boost them all--it won't pust them quite as far as it would if only some of the cores were in use, but it would work to leave no potential performance on the table.

Further architecture enhancements include AES instructions for hardware-accelerated encryption and AVX instruction for improved floating point performance (this will benefit video- and photo-processing tasks, as well as some financial applications). Intel’s Sandy Bridge platform already offers both of these instruction sets, so Bulldozer plays catch-up to some extent here.

AMD also baked in support for FMA4 and XOP instruction sets, which lend greater performance to complex mathematical operations. There’s a large can of worms lurking there, with Intel and AMD in disagreement over the optimal instruction sets for these operations. But that’s beyond the scope of my testing here.

On to the CPUs!

There will several models available at launch; here they are, in chart form.

The Bulldozer CPUs are compatible with AMD’s recently launched AM3+ socket. On the high end is the FX−8150 processor: It’s an eight-core chip slated to cost $245, with a standard clock speed of 3.6GHz that bumps up to 3.9GHz in Turbo Core mode, and tops out at 4.2 GHz in Max Turbo mode. AMD provided one of these CPUs for my tests, as well as an Asetek liquid CPU cooler for gauging overclocking performance.

It’s a nice lineup on paper--of special interest to me is the FX-4100, which offers half as many physical cores as its beefier siblings, but comes costs only $115 as of this writing. I suspect the FX-4100 will be a popular part in some of the more inexpensive gaming rigs that make the rounds in the coming months. Meanwhile, the FX-8150 will match up against the middle of Intel’s Sandy Bridge lineup, the Core i5-2500K.

My AMD test system consisted of the aforementioned Bulldozer CPU on an Asus Republic of Gamers Crosshair V Formula motherboard, with 4GB of DDR3-1600MHz RAM, a 1TB hard drive, and a Radeon HD 6970 graphics card. My Intel testbed was nearly identical, with the exception of the Core i5-2500K processor and the Intel DP67BL motherboard.

Enough talk: how does the FX-8150 stack up?