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

Smartphone SoCs use CPU cores 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 manufacture these chips.

ARM cortex cores use RISC (Reduced Instruction Set Computing). They handle less complex tasks or split difficult tasks into smaller sections before processing them. This differs from Intel and AMD CPUs on PCs that use CISC (Complex Instruction Set Computing) and can blaze through any task at once.

They are the only company that designs 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. Companies are not allowed to adjust or modify any part of the design. This means that you must not tamper with the design if you buy a core license from ARM. You must manufacture the CPU core according to ARM’s design and use it or sell it to the smartphone producers. Examples of core licensees are Google, Mediatek, JLQ, and Unisoc.

2. Architecture license

An architecture license allows an OEM to modify the CPU to its taste before use. When you buy an architecture license from ARM, you can tamper with or customize the design and create a CPU core that suits your needs.

People call these modified processor cores “custom cores” and they usually perform better than 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 CPU core can either work on tasks independently or join forces 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 Core Arrangement on a Smartphone’s 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, and consume a lot of battery.
• Big cores: powerful, used for heavy tasks, consume a good amount of battery. They’re also known as performance cores.
• Small cores: weak, used for light tasks, doesn’t consume battery at all. They are more commonly known as battery efficiency cores.

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 follow the big.LITTLE method. This method divides the CPU cores into big and small cores. The small cores, which are less powerful, handle easy tasks like texting, chatting, or watching a movie. The big cores, which are more powerful and faster, handle difficult tasks like playing HD games (e.g. PUBG or Fortnite).

This method arranges the cores into two distinct groups based on performance. The big cores deliver high performance but heat up and drain a lot of battery. The small cores save battery but are only good for small tasks. Your phone would overheat and your battery may not last long if you used the big cores all the time. For example, your battery lasts longer when you watch movies than when you play 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 an 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 is 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.

The Cortex X tier, the A70 tier, and the A50 tier make up the big.LITTLE and DynamIQ arrangement of cores. The Cortex X tier is the fastest and most powerful; the A70 tier delivers moderate to high performance but drains more battery; and the A50 tier handles low-performance tasks (like making calls or watching movies) that conserve battery life.

CLOCK SPEED

Clock speed measures how long a processor core takes to fetch data from your phone, decode it, and execute it to produce an output (fetch-decode-execute). For example, when you chat and hit A on your keyboard, your processor core fetches that instruction from the keyboard, decodes it, and then sends the letter A to appear on your screen. Clock speed is the time it takes to complete the fetch-decode-execute phase. It is measured in Hertz (Hz).

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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 A57).

Conclusion:

All CPU cores on smartphone SoCs today (both normal and custom cores) are built off the designs of the cores listed above in the table. These include both the normal and custom cores.

So next time you are getting a phone, do well to check these specs. A decent phone should have high-performance cores of cortex A73 or A75 and a good phone should have Cortex A76 or A78 CPU cores.

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