RISC-V Architecture: how a clean instruction set became a serious threat

Source: Dev.to

What an architecture actually defines

An instruction set architecture defines:

• the instructions a CPU understands
• register layout
• privilege levels
• memory ordering rules
• how software talks to hardware

It does not define:

• pipeline depth
• cache design
• clock speed
• manufacturing process

Two RISC‑V CPUs can run the same program and still be completely different internally.

Why RISC exists

RISC means Reduced Instruction Set Computing. The idea is to keep instructions simple and predictable so compilers and hardware can be efficient.

Compared to this:

• x86 – complex and full of legacy behavior
• ARM – RISC but controlled and licensed

RISC‑V keeps the RISC philosophy but removes ownership.

The base instruction set

Every RISC‑V CPU starts with a base ISA.
RV32I and RV64I are the foundations.

• RV32I – 32‑bit integer instruction set
• RV64I – 64‑bit integer instruction set

The base includes:

• integer arithmetic
• control flow
• memory load and store
• 32 general‑purpose registers

There is no multiplication, floating‑point, or atomics in the base; those are added only if needed.

This is why RISC‑V works well for tiny chips.

Extensions are how RISC‑V scales

RISC‑V is modular. Features are added using extensions.

Common extensions:

• M – multiply and divide
• A – atomic instructions
• F and D – floating‑point
• C – compressed instructions
• V – vector processing

A Linux‑capable system usually supports RV64IMAFDC.

This means the CPU includes only what it needs—no wasted complexity.

Registers and calling conventions

RISC‑V has 32 integer registers. Some examples:

• x0 – always zero
• x1 – return address
• x2 – stack pointer

Nothing is hidden or special without documentation, which simplifies compilers, debuggers, and OS kernels.

Privilege modes and operating systems

RISC‑V defines three privilege levels:

• machine mode – firmware
• supervisor mode – kernel
• user mode – applications

This matches modern OS design perfectly, making Linux support straightforward.

Linux runs natively on RISC‑V with full kernel support.

Memory model

RISC‑V uses a relaxed memory model. Instructions may be reordered unless explicitly prevented, improving performance and scalability but requiring correct synchronization.

The design is similar to ARM, not x86.

Microarchitecture freedom

RISC‑V does not force a single CPU design. Implementations can be:

• in‑order or out‑of‑order
• single‑core or many‑core
• tiny microcontrollers or server CPUs

The same software can run on all of them.

Operating systems that support RISC‑V

Fully supported operating systems

• Linux
• FreeBSD
• Zephyr
• RTEMS

Experimental or partial support

• Android
• Research Windows ports

Linux support is the most important signal of maturity.

Real RISC‑V processors available today

Embedded and microcontroller level

• ESP32‑C3
• ESP32‑C6
• Microchip PolarFire SoC

Linux‑capable processors

• SiFive Performance series
• Alibaba T‑Head Xuantie

These chips boot Linux and run real workloads.

Who should use RISC‑V

RISC‑V is ideal for:

• custom silicon designers
• embedded and IoT devices
• governments and public infrastructure
• research and education
• long‑term platforms avoiding vendor lock‑in

It is not ideal yet for:

• high‑end consumer desktops
• gaming systems
• proprietary driver‑heavy environments

Why RISC‑V is succeeding where others failed

Unlike Intel Itanium, RISC‑V does not try to replace everything at once. It grows gradually, coexists with existing ecosystems, and does not force migration. That incremental approach is why it is working.

Final thoughts

RISC‑V is not exciting because it is fast today; it is exciting because it is free, simple, and stable. It is an architecture designed to last decades, making it one of the most important CPU designs of our time.