Understanding Smartphone processors

Understanding Smartphone processors

The next generation of smartphones are set to get dual-core processors with improved graphics. We take a look at just what makes a smartphone processor

Smartphone processors have been the subject of much talk in the past week, as both Samsung and LG have announced plans for dual core phones in the coming months. LG is going to be using NVIDIA's Tegra 2 processor, while Samsung has cooked up its own processor, dubbed Orion.

The Tegra 2 and Orion  join previously announced dual-core processors from Qualcomm and Texas Instruments on the forefront of smartphone technology.

All of these processors use the same CPU design, licensed from the UK-based designer ARM. Much like Intel's near ubiquity in PC processing, ARM's processor cores have dominated the mobile world. In fact, ARM originally stood for Acorn RISC Machine and its CPU design has a heritage that dates back to the eighties and the classic BBC Micro and Acorn Archimedes computers.

This RISC architecture eventually lost out to the Intel x86 architecture in the PC space, but it continued to thrive in devices like PDAs and Phones. ARM cores ended up inside such iconic devices as Apple's Newton and iPod, Nintendo's Gameboy Advance and DS, 3DO's 3DO, Canon's EOS 5D Mark II camera and Amazon's Kindle DX.

ARM's most current CPU family is known as Cortex A9. These CPU cores are used in Orion and Tegra 2 processors. Where confusion often lies is in this relationship between the 'CPU' and the 'Processor' inside a smartphone.

In a traditional desktop PC the CPU, RAM, Graphics card and storage all plug into a motherboard, which has discrete chips to control Audio and Input/Output functions.

Inside a smartphone most of the space is taken up with battery and the luxury of spreading functionality between different chips isn't an option, nor is such a design very power efficient. Instead mobile phones use what's called System On a Chip (SOC) approach to processor design.

System on a Chip refers to processors that incorporate as many functions as possible in a single package.

At its most basic a mobile processor will incorporate both CPU and graphics cores. In the case of the Hummingbird processor from Samsung, which is used in the Galaxy phones and Galaxy Tab tablet and also forms the basis of Apple's A4 processor, used in the iPad and iPhone 4, it is an ARM Cortex A8 processor core with a PowerVR SGX 535 graphics chip. NVIDIA's Tegra 2 uses a similar design, pairing two ARM Cortex processor cores with an NVIDIA-developed graphics core.  

NVIDIA's Tegra 2 is a good example of a SOC design. It has two Cortex-A9 cores for CPU tasks, GeForce graphics chip for GPU functions and a variety of other cores designed to run the video and audio functions of a smartphone or tablet.

Most of these kinds of chips support something called Package on Package or Multi-Chip Module (MCM). This refers to a design where the silicon chip is packaged in a way that a memory chip can sit on top of it. This is not as fast a adding the memory directly to the processor, but it is still fast and a much more efficient use of space to stack chips in this way.

This is drilling down to a level of detail beyond what one needs to know about the processors on smartphones, but it is important to realize the process behind the design. Despite the fact that every major smartphone uses ARM's processing architecture, the actual silicon chips come from a variety of manufacturers. These silicon implementations of ARM's designs, and importantly the choice of graphics processor, will ultimately determine how a smartphone will perform.

It is for this reason that the source of a phone's processor is important. The battle between NVIDIA's Tegra 2 and Samsung's Orion is going to be quite heated, and it comes down not just to the ARM cores but the underlying graphics performance. Curiously both Samsung and LG touted a fivefold increase in graphics performance when announcing their products this week - we now play the waiting game to see just how true this statement is.

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