OnQ

Core of the matter: Is octa always better than quad?

2016年6月1日

Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries.

CPU cores are one of many components of a mobile processor. When you play level after level (after level) of Candy Crush, you use your smartphone’s CPU and GPU. When you text on WhatsApp, it’s the CPU and LTE modem. In fact, you tapped the CPU to open this webpage.

The CPU plays varying roles, often working alongside several of the other technology blocks, like the ones mentioned above. Given that it touches so many experiences, it’s understandable that the CPU is an important part of the mobile processor.

Primary school mathematics teaches us that eight is greater than four, but that doesn’t necessarily mean that an octa-core CPU is always better than a quad-core. Most people will look for the number of cores in the CPU and how fast they run (frequency) as a proxy for overall performance. However, not all CPUs or the cores within are the same. Here we’ll help you understand some the magic behind your smartphone.

Different Architectures, Different Performance

With respect to architecture, this isn’t Rome’s Pantheon or Frank Lloyd Wright’s Fallingwater house. We’re talking about CPU architecture. Here it’s about how the architecture is responsible for performance increases and improving the user’s experience as it moves from one generation to the next. And it should come as no surprise that different CPUs have different architectures for different purposes.

When it comes to smartphone processor designers, many companies, including Qualcomm Technologies, license the CPU core. This type of CPU is already designed and ready to be placed into the overall processor or System-on-Chip (SoC). However, we don’t stop there. We also create custom architectures purpose-built for high-end performance and power efficiency.

“Core” Capabilities

Not all cores are created equal, though. Different architectures and design trade-offs mean different CPUs will offer varying degrees of performance and power. Some CPUs are designed with ample horsepower to tackle the most intense task possible in the shortest amount of time. Others are designed to extend battery life by consuming the least amount of power possible. This means that, at the same frequency, a high-performance CPU will perform much faster than a power-efficient CPU.

The average car buyer isn’t going to ask the salesmen to see cars with four cylinders. Likewise, why would someone buy a phone based on the number of cores?

As an example, let’s look at two cars with four-cylinder engines, each built for completely different purposes: the Toyota Prius and the Alfa Romeo 4C, Imagine that the engine is the CPU and the cylinders are the cores.

The fuel-efficient hybrid, the Prius, reaches a top speed of just over 100 mph. The sleek-and-sporty Alfa Romeo hits a top speed of 160 mph. The Prius is supposed to be efficient; the Alfa Romeo is built for speed. When you’re looking to buy one of these cars, you either want efficiency or performance. The average car buyer isn’t going to ask the salesmen to see cars with four cylinders. Likewise, why would someone buy a phone based on the number of cores?

With our powers combined

Now let’s talk about multiple cores with varying capabilities. Today’s mobile processors can come with four, six, and eight CPU cores. To complicate matters further, the architecture and capabilities of those cores might not be the same. Many CPUs will mix and match high-performance and low-power cores in varying combinations. 

This is why counting cores alone is not a reliable way to judge performance. One octa-core CPU may only have low-power cores whereas another octa-core may use four high-performance and four low-power cores. Again, think of the Alfa Romeo and the Toyota Prius.

For any performance application, it is obviously recommended to have at least two high-performance cores. That’s where the hexa configuration comes into play. Because many mobile apps have two threads or less, these two high-performance cores will deliver high-performance for most use-cases, and then fall back to the low power cores when not needed. So in many scenarios, a hexa configuration will outperform an octa core with only power efficient CPUs.

Roadmap

Let’s take a look at how that has manifested in the Qualcomm Snapdragon processor tiers. In the Snapdragon 820 processor, we use our custom Kryo architecture. This is a quad-core solution, with two high-performance cores and two power efficient cores, each group runs at a different speed.

In the Snapdragon 600 tier alone, we have the three different configurations. The Snapdragon 652 has four big cores, the Snapdragon 650 has two, and the Snapdragon 625 has only little cores. 

In closing

Cores come in different shapes and sizes, with different capabilities and configurations, and varying performance and power. When shopping for your next device, remember to assess the capabilities of the whole processor first, of which CPU is only but one component. When you assess the CPU, remember to look beyond the core number, and into the type of cores.

Qualcomm Snapdragon is a product of Qualcomm Technologies, Inc.

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