Summary: With street prices hovering in the $250 range, AMD's Phenom 9600 Black Edition is priced aggressively. But how well does the CPU overclock, and what kind of gaming performance should you expect? Join us, as we take a detailed look at OC'ing the processor with AMD Overdrive!
That was four months ago. Since then, AMD has slowly ramped up production on the Phenom. And while the company has yet to unveil a new model of its quad-core darling, it did recently let loose a “Black Edition” of the flagship Phenom 9600 running at 2.3 GHz with an unlocked clock multiplier. The word over at AMD is that we’ll see new speed bins of the Phenom soon, along with a fresh spin of the silicon that fixes the errata number 298—the TLB issue said to plague all of AMD’s quad-core chips.
Until then, the principal competition to Intel’s line of desktop CPUs remains the AMD Phenom at either 2.2 GHz or 2.3 GHz. If you’re an enthusiast with aspirations of adding value through overclocking, that Phenom 9600 Black Edition is probably your best bet. Now, I know what you’re thinking. The Phenom hasn’t even been out six months yet and it already has a reputation as a mediocre overclocker. Why would an enthusiast choose this chip for his gaming platform?
There are a couple of reasons, actually. First, you have the 790FX chipset, loaded with advanced functionality and the latest performance features. Then you have price—one of AMD’s only defenses against Intel’s superior performance position. The Black Edition Phenom sells for $251. Though there are certainly faster Intel offerings, they’re also priced to reflect that fact. An enthusiast chip with an unlocked clock multiplier is unheard of at such low cost.
OverDrive: Yet Another Reason
Each of the four cores comprising a Phenom processor has its own 128KB L1 cache and its own 512KB L2 cache. The four L2s empty out in a shared 2MB L3 repository responsible for holding data that gets flushed from L2 and might need to be used later. All of that cache, together with the processor’s quadrupled execution resources, gives the chip a transistor count in excess of 460 million.
While much of that complexity is attributable to cache memory, AMD has also made significant improvements to the processing cores themselves in order to help bolster performance. For instance, the engine responsible for handling SSE operations is now 128 bits wide instead of 64 bits, so now all SSE operations are executed in a single cycle. Similarly, instructing fetching increases from 16 bytes per cycle to 32 bytes. And data moves faster in and out of the L2 cache thanks to more bandwidth between cache and the northbridge.
All of AMD’s chips already enjoy a significant advantage when it comes to communicating with RAM. An integrated memory controller goes a long way to help minimize latency. Phenom’s memory controller is revamped to further speed up data transfers. Instead of the dual-channel, 128 bit controller the K8 architecture employed, Phenom splits the logic into a pair of 64-bit controllers operating more efficiently. When you look at the boot screen of your Phenom-based platform and wonder why it’s reporting 2GB of memory at 64-bits when you clearly dropped your 1GB modules into separate channels that should total 128, remember that the modules are running in a dual, unganged 64-bit arrangement. Don’t worry—that configuration is the one you’ll want to use for the best possible performance. On top of offering more granularity, Phenom’s memory controller also incorporates support for frequencies up to 1066 MHz.
The Phenom drops into a brand new socket interface that isn’t all that new after all. Socket AM2+ is pin-compatible with the AM2 interface already in use. It adds support for a HyperTransport 3.0 interface between the CPU and northbridge, pumping up frequency from 1 GHz DDR to 1.8 GHz DDR. The resulting boost to bandwidth helps enable the PCI Express 2.0 links you’ll find on most Phenom-based platforms. You can drop a Phenom chip into an older AM2 board (with a new BIOS, of course), but you won’t get those HyperTransport 3.0 link speeds. You can also drop an AM2 processor into an AM2+-equipped motherboard to the same effect. Optimally, though, you’d pair AM2+ chip to AM2+ motherboard. For our purposes today, we’re using AMD’s 790FX chipset, the flagship of the company’s core logic lineup.
Notice that AMD is swinging at Intel with a 65nm process when Intel’s already enjoying the fruits of a 45nm process. How is it possible for the Phenom to compete given an inherent disadvantage like that? Interestingly enough, each of a Phenom processor’s four cores is able to operate using independent clock speeds and voltages, continually optimizing for the load you’re putting on the chip. AMD tags the Phenom 9600 Black Edition with a 95W TDP, less than Intel’s Core 2 Quad Q6600—closest to the Phenom in terms of price.
Of course, we all know that tech specs and architecture are great for coming up with theoretical guesstimates of how a given chip should perform or compare against its competition. The rubber meets the road when you get down and dirty with the hardware in real-world benchmarks.
OverDrive In Depth
The first time you fire up into OverDrive, you’ll find yourself in Novice mode looking at a summary screen with information about your CPU, memory, cache, and HyperTransport link. Click one screen over to the Status Monitor and you’re treated to a read out of the speed, voltage, and temperature of the Phenom’s four cores. GPU and board-level frequencies are also reported.
Shift over one more tab for a first taste of Windows-based performance modification. In Novice mode, you have a slider numbered from 1 to 10 corresponding to more aggressive overclocks. A Detailed Settings screen underneath lets you know exactly what changes were made. Three sub-menus provide options to Benchmark your tweaks, run a Stability Test, and Auto Clock the platform. Hit the Start button under that Auto Clock menu and OverDrive starts incrementally increasing the reference clock until the system fails its stability test. Talk about an easy way to crank out extra speed, even if you don’t have an intimate familiarity with overclocking.
The last menu screen, Preference, gives you the option to switch over into Advanced mode. Flip back to the Performance Control window, now populated by a very granular Clock/Voltage sub-menu. Here’s where the veteran hardware enthusiast can work his magic. An array of sliders lets you tune every frequency imaginable and seven different voltages. A Memory tab facilitates complete control over the timing of your modules. And of course, the Benchmark and Stability Test menus let you put those tweaks to task.
I went back and dropped the multiplier to 12x and sought a bit more horsepower from the HyperTransport interface, bumping the reference clock to 208 MHz. Again, I was looking at a 2.5 GHz CPU clock. Now the system also had extra speed from the memory, northbridge, and HyperTransport 3.0 connection, too.
Just to make sure the OverDrive settings were good to go, I applied the settings and restarted the test bed. OverDrive loaded back up and—what’s this? My adjustments had all reset? Ah ha; OverDrive Assist hadn’t yet been enabled. If you want your overclocked settings to be applied automatically, you’ll need to have that feature turned on.
Once it came time to start running benchmarks, the OverDrive-enabled configuration proved unstable, failing to consistently load the clock multiplier settings I had chosen and freezing up upon launching certain tests. Back to the BIOS I went, manually configuring the settings to match what I knew worked. In the end, I decided to stick with a 12.5x clock multiplier and stock HT setting. Interestingly enough, even with a pair of DDR2-1066 modules running at pre-configured SPD settings and pumped up with an extra .5V, I couldn’t get the platform stable using a 5.33x memory multiplier. The results were much better at DDR2-800 frequencies and more aggressive timings. Looks like the BIOS is still your go-to once you’ve figured out the best possible combination of settings with OverDrive.
Don’t think that OverDrive will save you from ever digging into your board’s BIOS, even if you do use it as a primary overclocking platform. The Gigabyte MA790FX-DS5 board we used for testing came loaded with software features, including a switch for disabling the TLB erratum, Cool’n’Quiet control, and a virtualization toggle. The board’s MB Intelligent Tweaker screen gives you control over the same knobs and levers as OverDrive, so if you’d rather overclock that way, there’s no shame in going old school. Not all AM2+ boards are going to be as enthusiast-friendly, though. Should you find yourself constrained by your vendor’s choice in BIOS settings, OverDrive is a real savior.
For what it’s worth, it may turn out that some motherboard vendors don’t give you an option to turn off that TLB erratum workaround, since it can cause stability issues under heavy load, according to AMD. If you find yourself on a system without the option to disable the patch, simply head into OverDrive and click the little green button in the upper right-hand corner of the utility. Based on our experiences with the Gigabyte board and its BIOS toggle, when the patch is enabled (thereby hammering performance), that button is green. When it’s yellow or red, the patch is off. Tech Report’s Scott Wasson reports that when the button is red, there’s also a CPU-based power management option being disabled to further enhance performance.
Unreal Tournament III
Lost Planet: Extreme Condition
Half-Life 2: Episode 2
Company of Heroes
Call of Duty 4: Modern Warfare
OverDrive: Perhaps the brightest beacon on the Phenom’s horizon right now is AMD’s OverDrive utility. The app isn’t perfect, and even with the OverDrive Assist agent running we weren’t always able to recover our overclocked settings. But for the veteran overclocker looking for a well thought-out interface or the rookie who wants to click one button and let the software do the rest, AMD is onto something.
Relative Performance: If there’s one thing we see over and over again, it’s that games rarely reflect processing horsepower as you hit the big resolutions with the details cranked way up. At the same time, Intel’s Core 2 Quad Q6600 held its own against the 9600 Black Edition. The difference is that the Phenom is AMD’s fastest desktop chip, while Intel has several other options for enthusiasts willing to spend more money.
AMD Phenom 9600 Black Edition