CPU cores in smartphone SoCs

CPU cores in smartphone SoCs are CPUs inside them that are responsible for data processing. They are the brains of the SoC in particular and the phone in general.

In simpler terms, A CPU core is a processing unit within an SoC. This unit is the most important part of a smartphone. The processing power of a phone can be determined simply by looking at the CPU cores in Smartphone SoCs.

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Read: What is an SoC?

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If your phone’s SoC has decent CPU cores, you can then use your phone to carry out heavy tasks. These include: playing high definition games, loading heavy apps, using your phone with very little lag etc.

However, if your phone comes with below average or weak CPU cores, you may be unable to play high definition games on your phone. Even using Facebook or Instagram will give you a headache as the phone may lag badly.

ARM Holdings

All CPU cores in smartphone SoCs are designed by a company called ARM holdings. ARM holdings do not make cores or produce any chips. Instead, they produce designs for Mobile computing and sell them to the semiconductor companies that actually manufacture these chips.

ARM cortex cores uses RISC (Reduced Instruction Set Computing). This means that they’re designed to handle less complex tasks or tend to break difficult tasks into smaller sections before attempting to process them. This is different from Intel and AMD CPUs on PCs that use CISC (Complex Instruction Set Computing) which can simply blaze through any task at a go.

They are the only company that design CPU cores for smartphones. They sell in two methods:

1. Core license

A Core license only allows an OEM to use the CPU as designed by ARM. No adjustment or modification of any sort is permitted. This means that if you buy a core license from ARM, you are not allowed to tamper with the design. You will manufacture the CPU core the way it was designed by ARM and either use it or sell it to the companies that produce smartphones. Examples of core licensees are Google, Mediatek, JLQ and Unisoc.

ii. Architecture license

An architecture license allows an OEM to modify the CPU to their own taste before use.If you buy an architecture license from ARM, you would be allowed to tamper with or customize the design to produce a CPU core that meets your taste.

These modified processor cores are referred to as “custom cores” and in most cases, they outperform normal cores. Examples of custom cores are Krait and Kryo by Qualcomm Snapdragon, Mongoose by Samsung Exynos, Cyclone, Typhoon, Twist and Swift by Apple Bionic.

Every smartphone in use today uses one of these two types of cores. If you use a phone with a Snapdragon, Exynos or Bionic SoC, the CPU cores inside these are customized. If you use a phone powered by Kirin, Mediatek or Unisoc, then those are normal cores.

Core count

Inside an SoC, there are different numbers of CPU cores. Around 2015, it was very common for phones to have four (quad) CPU cores, in 2020, eight (octa) cores became the standard. By 2025, SoCs should have ten (Deca) cores as the standard.

Each one can handle tasks independently, or can be combined to provide more power for more CPU-intensive tasks. In normal use, a multi-core processor will see the cores share the workload of the OS and all your running apps without ever reaching their maximum clock speed. The result is a snappier, more responsive device, with better multitasking support, plus lower heat emissions and less power consumption.

Core type	Number	CPU arrangement
Single core	1	1
Dual Core	2	2, 1+1
Quad core	4	4, 2+2
Hexa core	6	2+4
Octa core	8	2+6, 4+4, 1+3+4, 1+2+2+3, 2+2+4
Deca core	10	1+2+3+4, 2+2+2+4, 2+2+6

CPU ARRANGEMENT in an SoC

Most SoCs today use multiple CPUs. These CPUs have different uses in the SoC. They’re usually divided into 3:

• Prime cores: Very powerful, only called up for very serious tasks, consumes a lot of battery
• Big cores: powerful, used for heavy tasks, consumes a good amount of battery
• Small cores: weak, used for light tasks, doesn’t consume battery at all.

These CPU cores have to be arranged in a way that’ll get the best out of them. There are two types of CPU arrangement:

1. big.LITTLE

Most SoCs today use what is called the big.LITTLE. In this method, the CPU cores are divided into big and small cores. The smaller less powerful cores handle easy tasks like texting, chatting or watching a movie while the bigger, more powerful and faster cores handle the more difficult tasks like playing HD games (e.g. PUBG or Fortnite).

This method is used because, the cores are arranged into two distinct groups based on performance. The big cores give high performance but tend to heat up and drain a lot of battery, while the small cores are only good for small task and they save battery too. If your big cores were in use all the time, your phone would over heat and your battery may not last long i.e. your battery lasts longer when you are watching movies than when you are playing games.

2. DynamIQ

DynamIQ works in the same way as big.LITTLE but offers more flexibility in the way CPUs can be arranged on an SoC. This means as opposed to two CPU clusters, we can have three or more on an SoC. DynamIQ is only ever used on high end SoCs.

ARM ARCHITECTURE AND CORES EXPLAINED

ARM cortex CPU cores come in data sizes of 32 and 64 bits as well as instruction sets of 16 bit thumb and 32 bit ARM. The larger the number, the better.

If you are buying a phone from a honest manufacturer, they’ll put the type of CPU cores in the advertisement. Some of us buying phones must have seen words like ARM cortex 53, 72, 73 etc.

Here are a list of all the ARM cortex cores currently in use:

 

Instruction sets

• The Cortex A5, A7, A8, A9, A12 and A15 cores implement the ARMv7-A architecture. They are now extinct.
• The Cortex A32, A34, A35, A53, A57, A72 and A73 cores implement the ARMv8-A architecture.
• The Cortex A55, A65, A75, A76, A77 and A78 cores implement the ARMv8.2-A architecture.
• The Cortex A510, A710, A715, X1, X2 and X3 cores implement the ARMv9 architecture.
• The Cortex A520, A720 and X4 cores implement the ARMv9.2 architecture.

In the big.LITTLE and DynamIQ arrangement: the X tier are the prime cores with the highest performance, the A70 tier are used as the big cores that give mid to high performance (which drains battery) and the A50 and A30 tier are used as little cores for low performance tasks (like making calls and watching movies) which conserves battery.

CLOCK SPEED

A clock speed is the time taken for a processor core to fetch data from your phone, decode it and execute it to produce an output (fetch-decode-execute). For example, if you are chatting and you hit A on your keyboard, your processor core will fetch that instruction from the keyboard, decode it and then send the letter A to appear on your screen. The time taken to carry out the fetch-decode-execute phase is referred to as the clock speed. It is measured in Gigahertz (GHz).

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Read: Instruction Set Architecture versus Clockspeed

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Some people erroneously use clock speed as a yardstick for determining the performance of a processor. This is not entirely true. You can only use clock speed to compare two SoCs, when they use the same type of cores. e.g. A53 vs A53. If you are trying to compare different SoCs using different cores, then the one with the more advanced architecture wins every time e.g. A57 vs A76 (A76 is better regardless of the clock speed of the A53).

Conclusion:
All processor cores used in smartphones today (both normal and custom cores), are built off the designs of the cores listed above in the table. So next time you are getting a phone, do well to check these specs. A good phone should have at least high performance cores of A73/75 and above.

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