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From High-End Desktop To Elite Notebook

GeForce GTX 580M SLI Vs. Radeon HD 6990M CrossFire
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Eurocom chose to arm our test mule with Intel's Core i7-990X, if only to show that the Panther is capable of accommodating the fastest (and most power-hungry) processor available. There are, of course, a few drawbacks to showboating with such a potent piece of hardware (mainly, heat and power use). However, this desktop replacement chassis is intended to run primarily from an AC outlet anyway.

Even as the chassis designer somehow found room for a 130 W CPU, desktop-class 240 W graphics cards are still beyond the power and thermal capacity of any notebook. And this is where AMD and Nvidia’s model numbering gets confusing, if not downright disingenuous. We've complained about this before, and we'll do it again. Both organizations like to name their fastest mobile parts as if they were equivalent to their fastest desktop products. Of course, they're not even close.

Here's one of the most egregious examples: while the desktop Radeon HD 6990 uses a pair of "Cayman” GPUs, the Radeon HD 6990M’s single “Blackcomb XT” graphics processor shares more in common with the company's mainstream Barts part at the heart of Radeon HD 6870 and 6850 cards. A quick look at the specs shows why.

Desktop vs Mobility Radeon Graphics
 Desktop Radeon HD 6990Desktop Radeon HD 6870Radeon HD 6990M
Transistors5.28 billion1.7 billion1.7 billion
Engine Clock830 MHz900 MHz715 MHz
Shader (ALUs)307211201120
Texture Units1925656
ROP Units643232
Compute Performance5.1 TFLOPS2.01 TFLOPS1.60 TFLOPS
DRAM TypeGDDR5-5000GDDR5-4200GDDR5-3600
DRAM Interface256-bits per GPU256-bits256-bits
Memory Bandwidth160 GB/s per GPU134 GB/s115.2 GB/s
TDP375 W151 W100 W


Small differences aside, two Radeon HD 6970s go into a single desktop-class Radeon HD 6990. Meanwhile, the Radeon HD 6990M is nothing more than a power-optimized, underclocked Radeon HD 6870.

Similarly, the former mobile flagship (Radeon HD 6970M) was based on the desktop Radeon HD 6850. Sorry guys, Cayman’s thermal envelope is still too great for notebook use.

Nvidia is guilty of overstating the size of its package, too. Its GeForce GTX 580M’s GF114 GPU looks strikingly similar to the GeForce GTX 560 Ti’s GF114. And, in this case, they even use the same name. Let’s take a look at how it compares to the desktop GeForce GTX 580.

Desktop vs Mobile GeForce Graphics
 Desktop GeForce GTX 580GeForce GTX 560 TiGeForce GTX 580M
TransistorsThree billion1.95 billion1.95 billion
Engine Clock607 MHz822 MHz620 MHz
Cuda Cores512384384
Texture Units646464
ROP Units483232
Compute Performance1.51 TFLOPS1.26 TFLOPS952 GFLOPS
DRAM TypeGDDR5-4008GDDR5-4008GDDR5-3000
DRAM Interface384-bits256-bits256-bits
Memory Bandwidth192 GB/s128 GB/s96 GB/s
TDP244 W170 W100 W


Both AMD and Nvidia base their high-end notebook GPUs on upper-mainstream desktop parts, as neither is capable of producing a high-end desktop GPU at low power. The days of notebook GPUs based on desktop parts bearing similar names flew out the window when dual-slot graphics coolers become mandatory on desktop cards. But there's still that problem when a buyer compares a compact desktop with a GeForce GTX 560 Ti to a desktop-replacement notebook with GeForce GTX 580M and he doesn't know the GeForce GTX 560 Ti is actually the more-powerful part.

This time around, AMD's misrepresentation is the more serious. Its Radeon HD 6990 is already a hot, loud beast on the desktop. We're not sure the idea of that in a mobile platform is even attractive.

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