Processing processors: What’s the score with multi-core?

Get the low down on the high-tech wizardry inside the Lumia 920 and 820.

If you’ve ever wondered what the score is with the multi-core processors inside smartphones, you’re not alone. You hear the term mentioned all the time, but how, exactly, are CPU cores utilized in a multi-core processor? Unfortunately, there’s no easy answer.
Processors like the Snapdragon S4, which power the Nokia Lumia 920 and 820, are astonishingly complex pieces of silicon, packed with advanced technologies that affect every aspect of smartphone use. Nonetheless, it helps to know the myths and truth about multi-core processing when you’re out buying your next mobile device.

What exactly is the core?

Simply put, a CPU core is one of a number of functional elements that make up processors, such as the Snapdragon S4. In addition to running your favorite apps, it’s called upon for practically every smartphone task you can think of. Sure, 3D games rely heavily on the graphics processing unit (GPU), while high-fidelity audio and HD video rely on the Digital Signal Processor (DSP) and the video engine, respectively. But every one of these scenarios route through the CPU cores at some point. In other words, cores are to a processor like a general is to its commanding army.

As you’d expect, a multi-core processor contains more than one core, typically two or four, but there is no technical limit to the number. Within certain limitations, each core can run any given task irrespective of other cores.

 Let’s bust some myths

It makes sense to assume that a dual core, such as the Snapdragon S4 MSM8960, is twice as powerful as a single core, and quad core is four times as fast. Unfortunately, this convenient formula is hardly ever correct. While going from single to dual and dual to quad does increase performance, it’s rarely the case that performance is doubled or quadrupled.

One reason is that most applications are single-threaded and thus are only utilizing one or two cores at a time. Only a few high-end games and multimedia editing applications are multi-threaded and can fully reap the benefits of multi-core. The other reason is that many of these processes are distributed throughout the processor, so you have to take into account the power of the GPU, memory bandwidth and speed, and software optimizations.

So how do they work?

Timo Joutsenvirta, Nokia’s Marketing Manager for Smart Devices, has come up with a great analogy to explain the difference of single, dual and quad core. Imagine a coffee shop as the processor and  the customers are apps that want coffee. The baristas, meanwhile, are the cores who serve it to them. A single barista pours coffee from one coffee pot to each customer at a time. If more customers demand coffee, the barista might not be able to serve coffee fast enough. In this case, the customer would need to wait.

Adding more cores

One way to solve the waiting problem is to double or quadruple the number of baristas. More baristas can serve many more customers at a time so that none of them need to push themselves beyond their physical limitations. However, increasing the number of baristas also has its drawbacks. A single coffee pot can only pour one cup of coffee at a time, leaving the other baristas pot-less until the first cup is poured. Adding more baristas (or cores) can have an incremental improvement, but it’s not exponential.

Why bother, then?

The easiest way for technology companies like Qualcomm to improve processor performance is to increase the clock speed (or how many instructions a processor can perform in a given amount of time). Unfortunately, increasing clock speed (MHz, GHz) can also increase power consumption and heat generation, which are big no-nos for smartphone users. So, one way of increasing performance without your smartphone sizzling in your pocket is to use multi-core technology.

This enhances performance by allowing applications, if they are advanced enough, to run on more than one core at a time. It also saves power as each core can be run on at a lower clock speed than on single core, thanks to a technology called Asymmetric Multi-Processing, found only on the Snapdragon S4.

The bottom line

Smartphone processors are definitely not created equal. You only need to look at the incredible ways the Snapdragon S4 helps makes the Nokia Lumia 920 an amazing smartphone to see that. However, when comparing devices, it’s clear we should take into account more than just the CPU core.

Hopefully, this has helped you get to grips with the ins and outs of multi-core. If there’s anything else you’d like to know, drop us a line below and we’ll do our best to answer.