INSTRUCTION SET ARCHITECTURE VS CLOCK SPEED

The word “clock speed” is very ubiquitous these days. Everyone tends to use it. I am sure that a lot of us must have had frustrating discussions with tech illiterates who are fully convinced that clock speed is the number one criteria for assessing SoC performances for smartphones.
Today we are going to look at two factors that determines the performance of processor cores and see which one is more important. These are : Instruction Set Architecture and Clock speed.


INSTRUCTION SET ARCHITECTURE (ISA)

An Instruction Set Architecture (ISA) or simply architecture is a list of commands that are supported by the processor in a smartphone. If you issue a command to your phone that is not included in the instruction set, it would be unable to carry out that instruction. Also if you tried to install, load or use an app that needs certain commands to function properly that are not included in the ISA used in building your SoC, either CPU cores or GPU or even ISP as well, such an instruction would be unsupported. This is why when you issue certain commands to your phone, the phone would reject such a command and display “error” or “this action is not supported”.

An Instruction set (Image credits: Researchgate.net)

Here is an example of how an instruction set looks like;

• Add – Join 2 numbers together arithmetically
• Compare – Compare numbers logically
• In – Input information from a device or app e.g. camera or keyboard
• Jump – Jump to designated RAM address
• Jump if – conditional statement that jumps to a designated RAM address.
• Load – Load information into RAM from CPU
• Out – output information to a device e.g. monitor/display
• Store – store information to RAM

The ISA is an abstract model of a working CPU core. The making of it is called an implementation. The ISA is a part of the computer processor that pertains to programming. It is also called machine language. It tells the processor what it is supposed to do as well as how to do it (commands).

ISA Versions

All smartphone processor cores are made using Reduced Instruction Set Computing (RISC) by ARM. The RISC used for smartphones is called Arm architecture and it comes in several versions. The newer versions are always better and support more commands and instructions than the previous versions. They are Armv8-A, Armv8.1-A, Armv8.2-A, Armv8.3-A, Armv8.4-A, Armv8.5-A and Armv8.6-A.


CLOCK SPEED

There are certain steps that a CPU core takes during the processing of data. It is called the fetch-decode-execute phase. The CPU fetches the data, decodes it and then executes the instruction on the data. The fetch-decode-execute phase is equal to one clock cycle. Clock speed (or clock rate) can be defined as the operating speed of a computer or its microprocessor, expressed in cycles per second (hertz). The clock speed determines how steps are completed in one sec. It tells how fast a CPU can performs it is measured in Gigahertz (GHz). If you are getting a phone, the speed should be at least 1.6GHz. Flagship phones can be as fast as 2.6GHz.


ISA vs Clock speed

Clock speed is only good for comparing the performance of two SoCs in the same family e.g SD665 vs SD660, Helio P60 vs P65, SD865 vs SD865+ etc. The ISA on the other hand tells the extent of a SoC’s abilities and capabilities. The ISA that a CPU core is built from is more important than the speed.
This is why an SoC built with Armv8.2-A will destroy an SoC built from Armv8-A regardless of the clock speed. SD660 with a clock speed of 2.2GHz is not as good as a Helio G90T with 2.0GHz.

SD 660 vs Helio G90T (culled from nanoreview.net)

When shopping for your next phone, do well to check what instruction set the SoC is built on. Always prioritize a newer instruction set over clock speed.


This brings us to the end of this blog post, if there are any questions or contributions definitely hit me with it in the comment section. Thank you for reading to the end.