The short answer: x86, Arm and RISC-V are instruction set architectures (ISAs): the contract between software and a processor. x86 is a complex ISA controlled mainly by Intel and AMD and dominant in PCs and servers. Arm is a simpler RISC ISA licensed to many companies and dominant in phones and embedded chips, now growing in laptops and servers. RISC-V is an open, royalty-free RISC ISA that anyone can implement, growing fast in embedded and custom chips.
People often compare these three as if they were chips. They are not; they are rule books that many different chips follow. Once you see them that way, the differences make much more sense. Here is how I would explain them.
- At a glance
- x86
- Arm
- RISC-V
- What this means for a VLSI engineer
Table of Contents
Part 1: At a glance
Part 2: x86
x86 dates back to Intel’s processors from the late 1970s and has kept backward compatibility ever since. Its instructions are variable-length and complex, so modern x86 chips translate them into simpler internal operations. Only a few companies can build x86 processors, mainly Intel and AMD, and it remains dominant in desktops, laptops and servers.
Part 3: Arm
Arm is a RISC architecture with simpler, fixed-length instructions, designed with power efficiency in mind. Arm Holdings licenses its ISA and ready-made CPU cores to other companies, which is why almost every phone and a huge number of embedded devices use Arm. In recent years Arm-based chips have also grown in laptops and data centres.
Part 4: RISC-V
RISC-V started at UC Berkeley and is now an open standard managed by RISC-V International. Anyone can design a RISC-V processor without paying ISA royalties. It is modular: a small base instruction set plus optional extensions for multiplication, floating point, vectors and more.
That openness has made it popular for microcontrollers, storage controllers, automotive and custom accelerators, and it is the most common choice for teaching processor design today.
Part 5: What this means for a VLSI engineer
- The ISA affects the front end of a processor (decode, and some of the execution units), but most of the hard design work, like pipelines, caches and interconnects, is similar across all three.
- If you want to learn processor design, start with RISC-V. It is simple, open and well documented, and you can build a working core yourself.
- Knowing at least one ISA well makes architecture interview questions much easier.
Practise this on VLSI Forge
I built VLSI Forge so you can write RTL in your browser, run it on a real simulator and check every signal in the waveform. Free, nothing to install.
FAQ
Is RISC-V faster than Arm or x86?
The ISA alone does not decide speed. Performance depends on the micro-architecture, the process node and the design team. There are fast and slow chips of all three kinds.
Can I design my own RISC-V CPU?
Yes, and it is a great learning project. A simple single-cycle RV32I core is very achievable for a student.
Why is x86 called CISC?
Because its instructions are complex and variable in length, unlike the simpler, fixed-length instructions of RISC architectures.
Will RISC-V replace Arm?
It is growing quickly, especially in embedded and custom chips, but Arm has a huge software ecosystem. Most likely all three will coexist for a long time.
