AMD's $300 6-Core CPU: Too Good to Be True?

Posted 04/27/2010 at 5:44am | by Gordon Mah Ung

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AMD’s new Thuban hexa-core CPUs come out swinging with prices that belie their size

If we’ve learned anything from years of watching action movies: You never, ever count out the underdog. Such is the case with perennial underdog AMD.

Bloodied, beaten, and bruised by months and months of Intel chips that outpaced its parts, AMD isn’t giving up. Instead, it’s hitting back with its own hexa-core CPUs and doing everything just short of yelling yippie ki-yay!

And now for the shocker: These hexa-core CPUs are affordable. Hell, one of the parts is practically budget-priced. Intel’s high-flying hexa-core Core i7-980X is $1,000. Contrast that with AMD’s new 3.2GHz Phenom II X6 1090T at $295. Want more? The 2.8GHz Phenom II X6 1055T costs $200. Yes, $200 for a hexa-core processor. So yippie kay-yay mother frakker, ineed!

Want even more good news? AMD’s new chip will be backward compatible with the vast sea of AM3, and even older AM2+, motherboards out there. We’re quite glad to hear this, because at one point the company told us it planned to jettison DDR2 support, which would have cut off the AM2+ folks. Fortunately, the company changed its mind and both new chips include DDR3 and DDR2 support.

Just like with those Hollywood action movies, this story wouldn’t be complete without an element of suspense: Are AMD’s Phenom II X6 processors capable of whopping Intel’s similarly priced quad-cores, or even its $1,000 wonder, the Core i7-980X? To find out, you’re going to have to read on.

What’s the best budget chip available today for those interested in getting good performance on the cheap? We’ll walk you through the top five chips and tell you which one to buy.

*Transitor count not released. Figure is derived from AMD’s hexa-core Opteron part

Under the Hood of AMD’s Phenom II X6

In many ways, AMD’s new Phenom II X6 isn’t all that different from the Phenom II X4 processors. Both chips are built on a 45nm process, have the same 125-watt TDP rating, and feature the same microarchitecture. Of course, the Phenom II X6 is far larger than a Phenom II X4. A typical Phenom II X4 is 258mm2. The Phenom II X6 is about 40 percent larger at 364mm2. Oddly, AMD wouldn’t disclose the transistor count of the Phenom II X6, but we’d guess it’s the same or pretty close to the hexa-core Opteron 2435 at 904 million. On the surface, it would appear that AMD just took a Phenom II X4 and glued on two more cores. It’s not quite that simple, though. The L2 cache of the new chip remains at 512KB per core. The 6MB of L3 cache is also the same as with the older quad-core. That’s actually a reduction since the 6MB of L3 is shared among six execution cores instead of just four. Whether that plays into the performance of chip, isn’t yet clear. But AMD has made some other changes to boost performance.

Turbo Boost, Meet Turbo Core

AMD’s top-end Phenom II X6 1090T has a lower clock than the Phenom II X4 965 BE, but AMD makes up for that, and addresses the lack of applications and games optimized for six-cores, by introducing a new Turbo Core mode. Turbo Core overclocks three of the cores in the CPU when threading loads are light. The 1090T will Turbo Core from 3.2GHz to 3.6GHz, and the 1055T will Turbo Core from 2.8GHz to 3.3GHz. The mode is transparent to the OS and works without the need of drivers. It’s also not as discriminatory as Intel’s similar Turbo Boost, where apps that hit only one core will get more of a boost than apps that hit two or three. AMD said its tests show that the biggest benefits come from the three-core increase in games and apps that have not been optimized for four or more quads. Folks who want to mess with overclocking limits and ratios for Turbo Core can do so using AMD’s OverDrive utility.

Keeping Things Compatible

AMD’s strength has been its ability to make new chips work in older motherboards. In the three years that Socket AM2+ has been out, Intel has retired Socket 775 and introduced two new sockets that are incompatible with each other. That AMD can get its newest Phenom II X6 to work in older AM2+ boards (and probably even a few AM2 boards, too) is a testament to good planning. The only limiting factor for upgraders with the new Phenom X6 is likely a board’s thermals: The board must support 125-watt processors for the user to expect long-term reliability. BIOS updates will also be required, but AMD says that at launch, no fewer than 160 boards will have BIOS updates available to support the Phenom II X6.

Make Way for the 890FX Chipset

With the new chip, AMD is also introducing a new chipset series: the 8 series. The top chipset from AMD is the 890FX, which will replace the 790FX chipset. The 890FX has a big leg up over its Intel counterpart, the P55 chipset, in the number of PCI Express 2.0 lanes the chipset supports. One of the problems we’ve run into with the P55 lately is the lack of available PCI-E lanes to pass data from USB 3.0 and SATA 6 drives. With many P55 motherboards, installing two GPUs into the x16 PCI-E slots will handcuff the bandwidth of USB 3.0 and SATA 6 devices. Not all boards are affected, but most are. With 42 PCI-E 2.0 lanes available in the 890FX chipset, you can easily run multiple GPUs as well as your other devices without being constrained. Compare that to Intel’s P55 chipset which features 16 PCI-E 2.0 lanes in CPU and a pathetic eight PCI-E 1.0 speed lanes in the P55 chipset itself.

The new 890FX also features the SB850 south bridge with native SATA 6 support for six devices. The one key item missing from the SB850 is USB 3.0. Most board vendors are instead integrating NEC controllers to add the feature.

Inside the Phenom II X6

AMD’s new Thuban core is essentially the Istanbul core used in the Opteron 2435. Packing roughly 904 million transistors, the monolithic core has controllers for both DDR2 and DDR3 embedded in it. While the Opteron that it’s derived from has up to four Hyper Transport links for multiprocessor configurations, Thuban uses just one HT link to connect to the chipset.

So Is It Fast?

We put Phenom II X6 up against Intel’s best and brightest

As always, this is where the rubber meets the road, and to get a good feel for where Phenom II X6 1090T falls, we compared it to a spate of chips including the $282 2.8GHz Core i7-860, the $200 2.66GHz Core i7-750, the $195 3.4GHz Phenom II X4 965 Black Edition, and, of course, the $1,000 3.33GHz Core i7-980X.

We used identical GeForce GTX 280 cards in all of our test platforms, along with the same graphics drivers. For the Athlon testing, we used the new MSI 890-FXA GD70 motherboard. A Gigabyte GA-P55A-UD6 powered the LGA1156 parts, and an Asus P6X58D Premium handled the chore for the LGA1366 procs. All of the dual-channel boards used 4GB of DDR3/1333 RAM, while the triple-channel boards had 6GB of DDR3/1333. Windows 7 Professional and matched 150GB Western Digital Raptor 150 drives were used in all the platforms.

For benchmarks, we ran more than two dozen tests to find the strengths and weaknesses of AMD’s new chips. The results are interesting, to say the least.