ARM Cortex A9 cores are relatively tiny and it's not too difficult to put a handful of them down on an SoC. NVIDIA did just that with its Tegra 3 featuring four ARM Cortex A9s. NVIDIA's design approach is unique in the industry in that it uses TSMC's 40nm LPG process rather than a strict LP process like many of its competitors. The G transistors are reserved for the CPU cores, while LP transistors are used everywhere else. Typically you'd build the entire SoC out of LP transistors as it's a more cost effective way to build a low power chip. NVIDIA believes that it can more efficiently hit its higher CPU frequency targets using LPG than if it used a standard LP process. G transistors are typically leakier but can scale to higher frequencies at lower voltages than LP transistors on the same process node. The tradeoff is typically that low frequency operation takes place at higher power than in an LP design.

To have its cake and eat it too, NVIDIA added a fifth Cortex A9 to Tegra 3 built using LP transistors (hence the LPG process, G transistors in a sea of LP). This fifth core would only be active during the lightest of workloads and be limited in frequency (500MHz). If your phone/tablet is idle, the four higher performance A9s power down and only the fifth companion core remains active. As you unlock your phone/tablet and get to work, the fifth core eventually hands off the work to one or more of the higher clocked A9s. This dynamic architecture is what NVIDIA called vSMP. 

Today  NVIDIA's vSMP is getting a rebrand. As of now it's called NVIDIA's 4-PLUS-1. Expect to see a few different Tegra 3 phones announced next week at MWC brandishing NVIDIA's new 4-PLUS-1 trademark.

Source: NVIDIA Blog

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  • douglaswilliams - Thursday, February 23, 2012 - link

    As I read Anand's flurry of SoC architecture and performance articles tonight on my (old) iPad I load up the page, and then it just sits there for a couple minutes while I read it. Then I scroll down a bit, and again it just sits there waiting for me to finish reading.

    A processor switching to a very low power core during times like that totally makes since. And 4-PLUS-1 sounds like it will make for catchy advertising.
  • tipoo - Thursday, February 23, 2012 - link

    Is anything different about the Nvidias implementation, or is it just ARMs big.LITTLE with a different name?
  • SydneyBlue120d - Thursday, February 23, 2012 - link

    Nope, this is proprietary stuff. big.LITTLE is a much more "elegant" approach, albeit somewhat similar as a "concept".
  • 8steve8 - Thursday, February 23, 2012 - link

    nvidia's is available now.

    A15/A7 big.LITTLE is coming when, xmas?

    personally I'm excited to see 28/32nm dual core A15's soon.

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