AMD FX: Energy Efficiency Compared To Eight Other CPUs

We've already seen AMD's Bulldozer architecture come up short in the performance benchmarks. However, the company also claims it made important improvements to power consumption. Can FX-8150 at least score some points in the energy efficiency department?

Utilizing power efficiently isn't just a fringe message from environmentalists any more; it's a more mainstream concern, even from enthusiasts who are tired of pushing tons of air through their systems just to keep 300 W graphics cards stable. Processor vendors are on-board, too. AMD and Intel both preach the message of doing more with less power (generally whenever it's most convenient).

The message is a good one, though. Multiply out millions of platforms around the world and a few watts shaved off of each has a significant impact on the global energy demand. It's a matter of common sense: draw as much power required for the task at hand, but as little as possible when the performance (or energy use) isn't necessary.

In that regard, how do AMD's latest FX processors fare in the energy efficiency department?

Before it was FX, AMD's top-end desktop family was referred to as its code-name, Zambezi. What we discovered in AMD Bulldozer Review: FX-8150 Gets Tested was that AMD was not able to close the gap between its own best effort and Intel's almost year-old Sandy Bridge architecture.

It didn't help that launch pricing on the new FX chips made them more expensive than competing Intel-based products that are generally faster. Worse still, what can only be interpreted as very limited supply is currently inflating the cost of AMD's existing line-up. Now, we're seeing FX-8150s selling for £200 at the top-end and -4100s going for £90 at the bottom.

What Does Efficiency Mean, Anyway?

AMD isn't hopeless in its first generation of the Bulldozer architecture, though. The company's architects continually talk about maximizing what their hardware can do per watt of power consumption. Much effort was put into shutting down logic when it's not in use, and optimizing for efficiency. If the FX processors can achieve what its designers say (and what benchmarks have a difficult time showing when you look at performance on its own), then it's just a matter of finding the right price point for these CPUs.

To use an old car analogy, we're looking to measure the MPG rating of this processor at a given speed.

Low energy consumption on its own doesn't directly translate to high efficiency. Especially in today's world of single- and multi-threaded applications, it's important to take different workloads into account. We'd argue that no desktop machine runs at full throttle 24x7, making idle behaviour incredibly important, too. We'd also go so far to say that big power consumption at full load is acceptable if a platform can get its task completed faster and drop back to idle (with its corresponding lower power use) yet again.

Benchmarks: Intel Sandy Bridge

Intel earned some well-deserved praise over the past few years for the efficiency of its Core processors and, even more so, the Sandy Bridge architecture (second-gen Core i3/i5/i7). In other words, systems based on those CPUs consume very little power at idle, and are also relatively energy-efficient under load.

We've already seen the performance numbers and know how that story ends. The question now is: how well does AMD handle efficiency with its new desktop flagship? Did the company's efforts to share certain on-die resources pay off with better over utilization of a nearly 2 billion-transistor design? Today we're comparing Zambezi to AMD's own Phenom II X4 and X6 products, along with comparable CPUs from Intel. How does AMD's top-end 125 W FX-8150 size up to its most potent competition, Intel's 95 W Core i5-2500K, in the efficiency department?