David and Goliath: the SoC in smartphones and the CPU in computers

Martin Jud

4.4.2018

Translation: machine translated

We spend our days typing on our computers and our smartphones without necessarily realising that the technologies of these two types of device diverge. In fact, the performance and architecture of the essential components are completely different.

The classic computer has an integrated processor, whereas the smartphone is equipped with a SoC ("System on a Chip") that brings together its main elements - processor, graphics card, memory controller or even Ethernet or Bluetooth interfaces - on a single chip.

The architecture of a processor

Why is it that your smartphone, which has more processor cores and a higher clock speed, performs no better than your old notebook? Because of its processor architecture. x86 and ARM are the two most common architectures. You'll find x86 in laptops and desktops , and ARM in smartphone SoCs.

While smartphones and tablets have brought RISC-family ARM processors to the fore in recent years, their development actually dates back to the 1980s. British company Arcon marketed its 32-bit, 4 MHz prototype in 1983. At the time, the acronym "ARC" stood for "Acorn Risc Machine". It now stands for "Advanced RISC Machine". Success was not long in coming, and mass production at a clock speed of 8 MHz began in 1986.

Different architectures

ARM processors were designed to consume a small amount of electricity and have simple instruction sets. X86 processors, on the other hand, are primarily designed for high performance and throughput. The differences between the two processor families are varied. They relate to computing power, electricity consumption and end-user software.

For what computing power were the processors designed?

In addition:
Unlike x86 CPUs, ARM CPUs include only three instruction categories.

• The memory access instructions (load/store)
• Arithmetic or logic instructions intended for register values
• Instructions intended to modify program flow (jumps, subroutine calls)

Power consumption

As the battery size of mobile devices limits its capacity, the power consumption of an SoC is a decisive factor. For example, the SoC in your smartphone consumes less than 5W. It almost never needs to be actively cooled, which saves even more energy.
In contrast, a high-end x86 processor can easily consume 130W due to its complexity.

Compare David and Goliath by coding a video

Comparing the two architectures doesn't really make sense, as each has its advantages and areas of application. But I'd still like to know how the performance of the processors differs. So I ripped the Sleepy Hollow DVD and converted it from MPEG-2 to H.264. In other words, I'm reducing this 6.3GB film to around 1400MB, and doing so at virtually the same quality.

The devices in my duel:

• A 2012 Lenovo X220 notebook with Intel Core i5 2520M, 2 cores, 2.50 GHz base clock speed (max. of 3.20 GHz in turbo mode)
• A Blackberry Priv smartphone from 2015 with Qualcomm Snapdragon 808, 6 cores, up to 2.0 GHz clock speed

I of course make sure that the same codec and bitrate are set on both devices. I convert the film at 1400 kbit/s (using decoding software) in one pass just to test (we normally do at least two to improve the quality of the video). I don't touch the audio tracks, I leave them in DTS format.

Converting on the notebook

I use VirtualDub. I leave the black border on the video in order to preserve these conditions on the smartphone afterwards (so I can't trim or crop the image).

My old Core i5 2520M spends about an hour on it. In 2002, the operation took eight hours with my Pentium. I let it convert all night.

Conversion on the smartphone

It's hard to find an application that doesn't crash or give me an error message when converting a 6.3GB file. I ended up choosing "A/V Converter".

My smartphone gets to work and manages to convert 10 frames per second. I wait 5 minutes before the app displays an estimated total duration of 4 hours and 3 minutes. [[image:13172508 "The smartphone needs four times as long as the notebook."]]

Summary

My test shows that the SoC of a smartphone cannot be compared to the CPU of a standard computer. The time it takes to perform the same operation on the smartphone illustrates just how little our trusty mobile companions can do.

On the other hand, SoCs perform very well for their low power consumption. My i5 microprocessor consumes 35W, which would be enough to power 7 SoCs. If they were all connected, they could convert faster with the same power consumption as my computer's CPU.

Martin Jud

Senior Editor

martin.jud@digitecgalaxus.ch

I find my muse in everything. When I don’t, I draw inspiration from daydreaming. After all, if you dream, you don’t sleep through life.

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