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From OLED to Tegra: Five Myths of the Zune HD

Myth 2: NVIDIA's Tegra processor leapfrogs existing mobile processors

Now that you're no longer in the dark on the oversold OLED, what about the Tegra processor used by the Zune HD: is it really the miracle chip that it is billed to be, both achieving spectacularly unprecedented performance and industry-leading power efficiency? Has Apple's expertise in developing ARM CPUs and in running its own CPU fab plant been outmatched by Microsoft's first foray into mobile devices with a functional web browser?

The Tegra is built by NVIDIA, leaving Zune fans to suggest that it delivers industry leading, desktop-gaming type graphics that far exceed the capabilities of industry-standard mobile graphics. However, Tegra isn't a scaled down version of NVIDIA's PC graphics GPUs. Instead, it's based on technology NVIDIA acquired in its purchase of fabless chip designer PortalPlayer in 2007.

If PortalPlayer sounds familiar, it's because Apple formerly used its system-on-a-chip parts to build MP3 players up through the 5G iPod and the original iPod nano. Apple accounted for 90% of PortalPlayer's business when it dumped the company in 2006, reportedly because the company was arrogantly jerking Apple around. PortalPlayer was devastated and never recovered.

When NVIDIA acquired PortalPlayer for $357 million the next year, Wedbush Morgan Securities analyst Craig Berger observed, "This deal comes as a surprise to us as we believe there are other semiconductor firms that offer more technology for less money," and added that NVIDIA apparently "thinks it has a better chance of penetrating Apple iPod (video) products if it owns and integrates PortalPlayer’s technology."

Apple, PA Semi, and the PowerVR deal

However, NVIDIA didn't ever get back into the iPod market. Instead, Apple began sourcing SoCs from Samsung, bought its own fabless chip developer by acquiring PA Semi for just $278 million, and secured a secret design license for Imagination Technologies' PowerVR SGX graphics cores.

So, while NVIDIA's Tegra grew from the humble origins of the chip powering the video 5G iPod, the iPhone 3GS and the latest iPod touch models feature a mobile-optimized GPU core descending from the Sega DreamCast. While Imagination's PowerVR GPU never made it into the desktop GPU market to rival the technology from ATI and NVIDIA, it has become the gold standard in mobile GPUs.

But the GPU is only half the story. Tegra uses a conventional ARM11 family CPU core (ARMv6), the same generation CPU core used by the original iPhone, the Zune, Nokia N95, and the HTC Hero. The Tegra's CPU/GPU package also uses DDR1 memory, introducing significant real world RAM bandwidth limits no matter how powerful the embedded GPU core is rated to be in theoretical terms.

In contrast, the modern Cortex-A8 used in the iPhone 3GS, Palm Pre, Nokia N900, and Pandora game console represents the latest generation of ARM CPU cores. It also employs a DDR2 memory interface, erasing a serious performance bottleneck hobbling the Zune HD's Tegra. It's difficult to make fair and direct comparisons between different generations of technology, but NVIDIA's own demonstrations of Tegra's ARM11/integrated graphics show it achieving 35 fps in Quake III. The same software running on Pandora's Coretex-A8 with SGX GPU core achieves 40-60 fps.

Tegra's Core Problem

Tegra is also being hyped as providing "8 processing cores," but this is nonsense as it simply counts logical blocks common to all embedded SoC parts as "cores." The CPU in the Tegra is a single ARM11 core. Even if the Tegra did supply multiple CPU cores, the Windows CE kernel used by the Zune HD doesn't support multi-core SMP so it couldn't make any use of them.

Other mobile devices use multiple ARM processors for efficiency or cost savings, such as the original iPods which idled along using two low power ARM processors, or the Nintendo DS, which uses an ARM9 and ARM7 to handle different functions independently. However, there is nothing in the supposed "multiple cores" of the Tegra that offers anything comparable.

NVIDIA promotes Tegra as being "Ultra Low Power," but its standard ARM11 CPU doesn't deliver anything that isn't available in other ARM designs, nor any special power savings over more powerful and modern processors like the Coretex-A8 in the iPhone 3GS and latest iPod touch.

Again, if you're wondering why Microsoft was able to score the NVIDIA Tegra "before" Apple, it wasn't due to any mobile industry clout or hardware experience on Microsoft's end, but rather simply due to the fact that Apple has its own resources for designing and building advanced, state of the art mobile processors, and didn't need to buy into the desperate hype NVIDIA is using to promote the runner up technology of Apple's former SoC vendor.

On page 3 of 3: The HD isn't for high definition