The processor is the brain of any computer, and it is constantly evolving to improve efficiency. A processor’s design determines how many instructions it can do and how fast and efficiently it can do them. RISC, RISC-V, and ARM are terms used in processor design to denote a type of processor using a specific type of instruction set architecture (ISA).
Although not commonly used in mainstream computers, these processors power smartphones, microcontrollers, single-board computers, and all kinds of IoT devices. Read on to learn more about them and their differences.
Explaining Instruction Set Architecture and RISC
It can be hard to understand the difference between RISC, RISC-V, and ARM if you don’t know how CPUs work and execute code. So, before we begin comparing the terms, let us first talk about instruction set architecture and how it differs from what your regular computer processor uses.
Whether it be a microprocessor, a microcomputer, or a regular desktop computer, their processors all use an instruction set architecture (ISA). An ISA is the part of the processor that contains all the basic instructions a processor can execute. These instructions are the building blocks of a computer program. They are usually not more complex than your basic addition and subtraction.
In general, there are two types of ISA circulating in the market. They are the RISC and CISC architectures. RISC stands for Reduced Instruction Set Computer, while CISC stands for Complex Instruction Set Computer. Both architectures are prevalent today, with x86 (Intel and AMD processors) being the top processor utilizing CISC and ARM (Qualcomm and MediaTek processors) as the most popular RISC architecture.
Basically, RISC is a computer architecture designed and optimized to use fewer instructions than its CISC counterparts. These fewer instructions and other optimizing technology used in RISC architecture allow these types of processors to use less power, making them ideal for smartphones, cameras, smartwatches, and all kinds of IoT devices.
What is ARM?
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We have established that ARM processors are some of the top RISC architecture in the market. So, what exactly is ARM, and why are they the most popular RISC processors?
Before RISC-V (which we’ll talk about shortly), ARM-based processors were the only option for anyone wanting to build an electronic product using their own custom processors.
Arm (with the lowercase “rm”) Ltd. is a company that designs and licenses chips for various hardware manufacturers, such as Apple, MediaTek, Qualcomm, and smaller companies like PINE64. They use their own closed-source ARM ISA to design highly efficient microprocessors and system-on-a-chip (SoC). All designs made by Arm are known as Advanced RISC Machine processors or simply ARM (all upper case) processors.
Aside from being one of the first companies to sell and custom-make chip designs, Arm has managed to be the dominant RISC chip designer because of its continuous innovations with the ARM ISA and ARM processor designs.
Much like AMD’s APU, which combines CPU and GPU into one die, ARM processors are known to combine CPU, GPU, Memory, DSP, and various modems all in one die or chip—this is called System on a Chip (SoC). This close integration of multiple modules has allowed the ARM processors to be fast and efficient.
What is RISC-V?
RISC-V is an open-standard ISA developed at the University of California, Berkeley. This ISA doesn’t introduce any new technology in the market, yet many speculate it is the future of RISC-based processors. So why is it?
RISC-V has gained attention from companies like Amazon, Google, Qualcomm, Intel, Rockchip, SiFive, Sony, ZTE, and Western Digital. This is because RISC-V is an open-standard ISA. RISC-V International (a non-profit association for RISC-V) allows anyone to use the RISC-V ISA on their processors without paying a fee.
The great thing about RISC-V is its ability to expand the instruction set based on whatever processes your chip will need for a given product. RISC-V only starts with a base instruction set of 47 instructions. These instructions include all the basic functionalities a chip needs to work and do basic tasks.
Designers will then be free to choose which instructions to add to the base instruction set to give the chip all the functionalities it needs without any extra bloat functionalities it wouldn’t use.
Although RISC-V is still a relatively new ISA, its potential to provide cost-effective and highly efficient specialized chips for various applications is what makes it a special ISA.
ARM or RISC V? Which is Better?
ARM and RISC-V are ISAs that follow the RISC design philosophy, so which one is better?
To compare, here is the performance comparison between SiFive’s P670 processor vs. Arm’s Cortex-A78 processor:
As you can see in the illustration, the Cortex-A78 is slightly ahead of the P670 regarding peak single-thread performance. Although the Cortex-A78 wins in raw performance, the P670 doubles the compute density of the Cortex-A78. This means that SiFive’s P670 processor provides comparable peak single-thread performance over the Cortex-A78, which is twice the physical size of the P670.
In this comparison, SiFive’s P670 processor wins over Arm’s Cortex-A78 for delivering comparable single-thread performance at half the size. However, you should also note that the Cortex-A78 was released on December 2020 through the Vivo X60 and X60 Pro, while the P670 was just announced on the first of November 2022.
That’s around a two-year difference in terms of research and development. Arm’s latest processors now run on the ARMv9 ISA, significantly improving the ARMv8 that the Cortex-A78 uses. To put that in perspective, the latest ARMv9 processors provide around 30% higher performance and are 50% more energy efficient.
So, in terms of raw performance, ARM processors are still in the lead. But with SiFive’s P670 providing twice the compute density over the Cortex-A78, RISC-V processors seem to have an advantage over ARM processors regarding wearable technologies which greatly benefit from using smaller-sized processors.
RISC, RISC-V, and ARM are Different Instruction Set Architectures
In summary, RISC is a design philosophy that uses fewer instructions than you would find on a regular desktop processor like the x86. Having shorter and fewer instructions allows RISC processors to be highly power efficient.
ARM is a closed-source ISA based on RISC that is licensed to companies for their processors and SoCs. The ARM ISA allows Arm to design high-performance RISC processors like Apple’s M1 chips. On the other hand, RISC-V is an open-standard ISA based on RISC that anyone can use to design their own chips without paying license fees. Its open-source nature allows the RISC-V ISA to be further modified and expanded to make specialized chips for specific tasks.
Although it might not seem to be all that important, this ongoing competition between ARM and RISC-V will surely benefit all consumers, especially when it comes to IoT devices, microcontrollers, single-board computers, and handheld devices such as smartphones and tablets. And who knows, with Apple's M1 chips as proof, RISC-based processors may actually compete with x86 processors sooner than expected.
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