What is the SoC?, Clock speeds

Welcome to the School of Android 501. Here, we will cover hardware related topics to help readers understand the components that go into smartphones and other mobile tech.

Android phones are riddled with specs. People exclaim various stats like children looking at Pokemon cards, “Check out this phone with a — MP camera!”, “This phone has 4 GB of RAM!”, “The world’s first deca-core smartphone is here!”. But what do all of these specs actually mean?

Here, we will be continuing our dive into what a SoC actually is. The first School of Android 501 article detailed what a 64-bit processor was and why they are preferred over a 32-bit processor.

You might want to check out that article first if you are not aware of what a SoC is in the first place.

This time around, we will be talking about clock speeds and what they refer to.

Finding and understanding clock speed

On your current device, you can run a app really quickly like Geekbench 3 or CPU-Z. Both apps will quickly provide a clock rate for your device.

Both apps read my Nexus 6 as a 2.65 GHz clock speed. What this translates to is the SoC can operate at a maximum of 2.65 gigahertz. Each gigahertz represents one thousand million cycles per second.

In the end, the Nexus 6 can max out at 2.65 thousand million cycles per second.

To break it down, 1 MHz will equal one million cycles per second and 1 GHz will equal one thousand million.

Smartphones with Snapdragon 801 | SpecOutAs you can see in the above comparison, most phones running the same SoC are clocked to the same speeds. All four phones with the Sanpdragon 801 are clocked at 2.5 GHz.

What is a cycle?

A cycle is a single repeating occurrence of the SoC’s processes. To make a simple example, we will look at the original Intel Pentium processor. The Pentium had a five-stage pipeline:

 

1. Prefetch/Fetch: Instructions are fetched from the instruction cache and aligned for decoding.
2. Decode1: Instructions are decoded into the Pentium’s internal instruction format. Branch prediction also takes place at this stage.
3. Decode2: Same as above. Also, address computations take place at this stage.
4. Execute: The integer hardware executes the instruction.
5. Write-back: The results of the computation are written back to the register file.

Each clock cycle, one process is completed at each step. Then they move on to the next step. The clock cycle determines how many steps are completed every second.

With this five-stage pipeline, each process will take five clock cycles to complete. The faster the clock speed, the faster the chip completes the cycle.

With this information, we know that chips with the same pipeline will benefit greatly from a faster clock speed, but that isn’t all there is to it.

Not all processors are created equal

While some chips can have a simple fire-stage pipeline, it is equally possible that a chip will have a 22-stage pipeline or any number of stages.

This means that those chips will require more clock cycles to complete the same amount of work as another chip with less stages.

What does all of this mean?

Bottom line, the clock speed doesn’t matter in your mobile device. Each chip of the same family is normally clocked at the same rate.

As you can see in the chart way above, all for Snapdragon 801 devices are clocked at a nice 2.5 GHz. If one device were to be clocked at 2.7 GHz, then it would yield better performance. Alternatively, if one device were to be clocked at 2.3 GHz, then it would take longer to do the same amount of work as another device.

However, most mobile SoCs are shipped at the same clock rate as all other devices shipping with the same SoC, so it really doesn’t matter.

This would be a good reason why manufacturers don’t make a big deal out of their devices clock speed. It is not a good way to determine performance.

In fact, it is basically impossible to predict performance based off of a clock speed because the clock speed only matters to devices with the same SoC, and all devices with the same SoC generally have the same clock speed.

Closing

In the end of the day, clock speed doesn’t really matter unless you are rooted and looking to overclock your device, but that is a lesson for another day.

If this article didn’t answer all of your questions, or left you with more questions than answers, feel free to leave a comment below. We will do our best to answer your questions for you!