You probably know this by now, since it seems pretty much everyone has read our initial review of AMD’s FX-8150 processors, but the “Bulldozer” architecture on which the FX chips are based is a “speed demon”—a CPU designed to run naturally at high clock frequencies. The concept is to do relatively less work per clock cycle and to enable higher speeds to make up the difference. You may also know that the FX-8150’s performance hasn’t entirely lived up to the “FX” product name—or to the expectations of many AMD fans. The reasons for that fact are many, but one of them seems to be fairly clear: Bulldozer-based chips probably haven’t reached the clock speeds AMD’s engineers originally intended.
We attempted to rectify that fact during our first round of FX CPU testing by cranking up the clock speeds, an effort made easier because all FX-series processors have unlocked multipliers. We were a bit frustrated to find out that we couldn’t nudge our chip past 4.4GHz without it turning flaky and crashing on us. However, we also had quite a bit of trepidation about pushing our brand-new, pre-release, 32-nm processor beyond about 1.46V.
Yeah, we were basically being wusses.
We were using a pretty formidable tower cooler at the time, but pumping that much voltage into a chip means it will be thinking deep thoughts about its own mortality before dropping off into C1E sleep. If you’re going to push that hard, it’s a good idea to have really effective cooling—maybe not just a biggish air cooler, but a truly large water cooling unit, with a radiator the size of Charlie Sheen’s liver and a pair of fans to match.
Fortunately, AMD seems to have been thinking along those same lines, because it has been making arrangements to include a beefy FX-branded water cooling unit (originally made by Asetek) in the box with certain FX processors. AMD says it will begin by bundling this cooler “with the AMD FX CPUs in select regions,” starting with Japan and “then rolling out into other regions.” We don’t yet have final word on exactly when this cooler might make it into North America, but we expect the bundle to add about $100 to the price of an FX processor alone.
The cooler is completely self-contained and pre-filled with coolant, so users won’t have to mess with filling or maintaining the fluid in the unit. Installing it is as simple as twisting in the four thumbscrews around the CPU socket, making a fan-sandwich out of the radiator, and plugging in a couple of headers on the motherboard. One of those headers powers the pump and fans, and the other is a USB connection for control and monitoring of the cooler. AMD supplies a software CD with a relatively simple utility that monitors the liquid temperature and fan speeds, along with allowing the user to choose one of the pre-existing fan control policies or to define his own.
Our mission was to see how far this fancy bit of kit would allow us to push an FX-8150 processor. At AMD’s recommendation, we chose the “Extreme” fan speed preset. Fluid and fan temperatures plummeted as Damage Labs was filled with a loud, Dyson-esque whine…
We took our prior plateau of 4.4GHz at 1.465V as a starting point for our renewed overclocking attempts. We were soon able to reach 4.5GHz and then 4.6GHz at 1.525V, which was encouraging. However, getting the chip stable at 4.7GHz required more voltage, forcing us to ratchet things up to 1.55V, the peak value exposed in AMD’s Overdrive utility—and a heckuva lotta juice for a 32-nm processor. Once at that voltage limit, we tried for 4.8GHz, but we quickly saw errors in Overdrive’s stability test.
So, 4.7GHz was it. That’s 1.1GHz above the FX-8150’s base clock, but only 500MHz beyond its peak Turbo Core frequency. Still, it’s not far from the projection in AMD’s press literature, which says AMD’s internal attempts with water cooling topped out at 4.9GHz (presumably with more than one chip on hand). 4.7GHz is also a couple of hundred megahertz higher than what we’ve seen from Intel’s Sandy Bridge and Gulftown, in our limited, air-cooled overclocking exploits with those chips.
Even at 1.55V, we weren’t pushing the FX cooler past it limits. During stability testing, CPU temperatures topped out at around 54.5° C, with an ambient room temperature of about 74° F/23° C. Yeah, the thing was incredibly loud—I’d give you a decibel number, but we’re currently having the roof replaced, and I don’t want to harm the workers’ ears. Er, I mean, all of the hammering would throw off the measurements. Still, the cooler itself could have taken more heat, had we needed it.
At those overclocked settings, our FX-8150’s power draw rose considerably from its stock levels. We did a quick measurement, in fact, and it came back like so:
That, my friends, is why AMD didn’t push any higher than it did on FX clock speeds. Cranking up the CPU voltage does bad things for power consumption. Although our motherboard, PSU, and cooler could apparently handle it reasonably well, an FX processor at these speeds goes well beyond the top established PC power envelope of 125W. Even resurrecting the old 140W power window probably wouldn’t have bought AMD much more in terms of frequency. There is headroom in this chip, but you pay for it dearly in wattage.
Oddly enough, the benchmarks we selected months ago for our overclocking performance tests seem to be pretty well suited to the Bulldozer architecture. Thus, turning up the clock frequency allows the FX-8150 to put up some really nice numbers, tying or beating a Core i7-2600K overclocked to 4.5GHz in several cases. There are some pain points here, such as the difference in single-threaded Cinebench performance between the FX-8150 at 4.7GHz and the Core i5-2500K at stock (scores of 1.16 vs. 1.48, respectively). Still, had Bulldozer landed at frequencies north of 4.5GHz within conventional power envelopes, the competitive landscape might look rather different. Indeed, if GlobalFoundries can manage to refine its 32-nm fabrication process to allow such speeds in the coming months, who knows?
For now, thanks to a formidable bundled cooler, those folks who bleed AMD green (or is it red now?) will have an option for achieving bragging-rights-type performance in some cases, so long as they’re willing to pay for it in the form of added heat, noise, and power draw.