Why do Mobiles have Two CPUs?

If you've paid attention to the specifics when buying a phone in the last decade, you might have noticed the confusing inclusion of two CPU listings. When systems like PCs have operated with one CPU for decades, this can make the inclusion more than a little confusing. So why do mobiles do this, and what are the implications to how your phone performs?

Fast and Slow

Before looking at the specifics of why two CPUs are included, we need to understand just how vastly the differences in CPU load can be. On the low end of the spectrum, consider online casino games like those in video slots UK websites. Accessing these websites means light browsing, and jumping into titles like Fluffy Favourites and Power of Thor Megaways. While these titles look great, they're also built on efficient HTML5 systems, so they don't require much CPU power.

"Mobile-ITX CPU Module-Feather" (CC BY 2.0) by viagallery.com

Compare this to a game like PUBG. With a huge arena and an enormous amount of 3D action taking place, mobiles have to crunch an immense amount of maths to get a game like this to function well. This means an enormous load on the CPU, RAM, and storage drives. These two different scenarios present two very different requirements, so why does this matter?

Hardware Specialisation

The most fundamental reason that mobiles have two CPUs is battery life, and how that relates to the different strains put on systems via high and low demand uses. CPUs take a lot of energy to run, and while it is possible to vary CPU speeds via underclocking/boosting, this approach is never anywhere near as energy-efficient as the two CPU approach.

In other words, running a faster CPU at all times, even when it's not being pushed, would drain the battery within a few hours. On the other hand, running a slower CPU at all times would mean that more demanding applications wouldn't run at all. Though a much larger battery could solve this problem in theory, it's been a long time since the brick phones of old, and the market isn't interested in going backwards.

Two CPUs means that the low power system will operate during general duties, and the high power one will kick in when necessary. This gives a kind of the best of both worlds, which, while not perfect, overcomes the issues the singular CPU approach would imply.

The other part of this concern is the thermals. A higher load on the CPU means more heat, which causes better cooling. Over time, high heat and temperature cycling can cause damage to components, and this applies just as much to mobiles as it does to desktops.

In the Future

As for whether we will ever solve the battery and heat problems, that much remains in doubt. As far as technology has come, energy density often doesn't keep pace. Though efficiency improvements occur, there are usually offset by increasing demands put on new cutting-edge hardware. While some sort of breakthrough developments could completely overthrow the status quo, current trajectories have nothing on the immediate horizon.

"Power bank" (CC BY 2.0) by EU2017EE

Just because there aren't direct solutions, however, doesn't mean there aren't ways to sidestep the fast CPU and battery drain problem. We've been saved more than once by power banks, which also make great tools for other devices in an emergency. It might not be a new CPU, but it's the best middleman current technology can provide.