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ARM Cortex-M

Summary
  • ARM (originally Acorn RISC Machine, now Advanced RISC Machines) is a family of RISC instruction set architectures, designed by Sophie Wilson and Steve Furber at Acorn Computers and first shipped in 1985.1
  • Arm Holdings (the company) doesn't manufacture a single chip — it designs and licenses the architecture and core designs, and other companies (Apple, Qualcomm, Samsung, NVIDIA, MediaTek, and dozens more) build the actual silicon.
  • It's the dominant architecture in mobile and embedded computing, and — via Apple Silicon and server chips like AWS Graviton — increasingly competitive in laptops and datacenters too.

Think of ARM as:

"A blueprint company, not a construction company — Arm Holdings draws up the plans (and sometimes a finished reference design), and lets dozens of different builders put up the actual buildings."

What Makes ARM Different

RISC (Reduced Instruction Set Computer) design favors a smaller set of simple, fixed-cost instructions over CISC's larger set of complex, variable-cost ones (x86 being the classic CISC example). ARM is also a strict load-store architecture — arithmetic and logic instructions only ever operate on registers, never directly on memory; a separate LDR/STR instruction has to move data between memory and registers first.2 Fewer, simpler instructions mean a simpler pipeline, which is a large part of why ARM cores have historically been so power-efficient — the trait that made them the default choice for battery-powered devices.

The other defining trait is the licensing model itself, and it comes in two different forms:

License Type What you get Who does this
Core (IP) License A ready-made Arm-designed core (e.g., Cortex-A78) to drop into your own chip Most SoC vendors — MediaTek, many Qualcomm designs, Broadcom
Architecture License The right to design your own custom core that implements the ARM instruction set Apple (all its own cores), Qualcomm's Oryon (via the Nuvia acquisition), historically Samsung (Mongoose) and NVIDIA (Denver/Carmel)

This is the key structural difference from x86: there's no single company building every ARM chip, which is exactly why "ARM" describes an entire ecosystem of very different silicon rather than one company's product line.

ARM Architecture Versions

The architecture version (always written ARMv#) is the instruction set itself — separate from any specific chip's name. This is the single most confused pairing in the whole ecosystem: "ARM7" and "ARMv7" are not the same thing, and don't even line up numerically.3

Version Year Key Addition Notable Implementation
ARMv1 1985 The original architecture — 26-bit addressing, ARM instruction set only Acorn's internal prototype, never sold commercially
ARMv2 1986 Multiply instructions, coprocessor support ARM2, ARM3
ARMv3 1990 Moved to 32-bit addressing ARM6, ARM7
ARMv4 / ARMv4T 1993 / 1995 ARMv4T added the Thumb 16-bit instruction set — better code density for memory-constrained systems ARM7TDMI, StrongARM
ARMv5 / ARMv5TE 1999 Enhanced DSP/multiply instructions, improved Thumb/ARM interworking ARM9E, ARM10E, Intel XScale
ARMv6 2001 SIMD media instructions, VFP (Vector Floating Point); ARMv6T2 added Thumb-2 ARM11, first-gen Raspberry Pi
ARMv7 2003–2005 Split into three profiles — Cortex-A/R/M — replacing the old ARM7/9/11 naming scheme Cortex-A8, A9; Raspberry Pi 2
ARMv8 2011 Introduced AArch64 — a full 64-bit execution state, alongside 32-bit AArch32 Cortex-A53, A72; Apple A7; Raspberry Pi ¾
ARMv9 2021 SVE2 (vector/DSP extensions), Confidential Compute Architecture, AI/ML-focused enhancements — built on top of ARMv8 Cortex-X2/X4, Cortex-A720

Table 1. ARM Architecture Version History

Version numbers don't reset per profile

Since ARMv7, each version actually splits into per-profile variants — ARMv8-A, ARMv8-R, ARMv8-M, and so on — because the application, real-time, and microcontroller profiles evolve together but don't need identical feature sets.

32-bit vs 64-bit: AArch32 and AArch64

Before ARMv8, everything was 32-bit. ARMv8 introduced two parallel execution states:4

  • AArch32 — the 32-bit state, backward-compatible with earlier ARM/Thumb code, using the A32 (ARM) and T32 (Thumb-2) instruction sets
  • AArch64 — a new 64-bit state, using the A64 instruction set, with wider registers (31 × 64-bit general-purpose) and a redesigned exception model

A modern 64-bit ARM chip can typically still run 32-bit AArch32 code for compatibility, though newer cores (and Apple Silicon specifically) have started dropping AArch32 support entirely to simplify the chip.

AArch64 vs. ARM64 vs. arm64

These all refer to the same thing. AArch64 is ARM's own official term; Apple, Microsoft, and much of the Linux world commonly just say arm64 or ARM64 instead.4

The Cortex Families

Since ARMv7, cores are named Cortex-[profile][number], where the profile tells you the target use case:5

Family Profile Characteristics Typical Use Examples
Cortex-A Application Runs a full OS, MMU, often out-of-order execution Phones, tablets, laptops, Raspberry Pi A53, A72, A78, X4
Cortex-R Real-time Deterministic, low-latency, hard real-time guarantees ABS/automotive control, hard drive controllers, modems R5, R7, R52
Cortex-M Microcontroller Smallest, lowest power, simple MPU instead of a full MMU Microcontrollers, IoT sensors, embedded control M0+, M4, M33, M55
Neoverse Infrastructure Server-grade, high core-count, throughput-optimized Cloud/datacenter server chips AWS Graviton, Azure Cobalt, Google Axion

Table 2. The ARM Cortex and Neoverse Families

Which one is in your device?
  • A smartwatch or a Bluetooth sensor → almost certainly Cortex-M
  • A car's ABS controller → Cortex-R
  • Your phone, a Raspberry Pi, or an M-series Mac → Cortex-A (or Apple's own custom AArch64 core)
  • The server behind a cloud API call → increasingly, Neoverse

Real-World Examples

Device Core Architecture
Raspberry Pi 1 ARM1176JZF-S ARMv6
Raspberry Pi 2 Cortex-A7 ARMv7-A
Raspberry Pi 3 Cortex-A53 ARMv8-A
Raspberry Pi 4 Cortex-A72 ARMv8-A
Raspberry Pi 5 Cortex-A76 ARMv8.2-A
Raspberry Pi Pico (RP2040) Cortex-M0+ ARMv6-M
Apple M1–M4 Apple-designed (architecture license) ARMv8-A / ARMv9-A
AWS Graviton Neoverse-based ARMv8-A / ARMv9-A

Table 3. ARM Cores in Common Devices

Useful Resources

  1. Wikipedia contributors. (n.d.). ARM architecture family. Wikipedia. https://en.wikipedia.org/wiki/ARM_architecture_family ↩

  2. All About Circuits. (2019, April 10). The Arm architecture explained. https://www.allaboutcircuits.com/technical-articles/arm-architecture-explained/ ↩

  3. WikiChip. (n.d.). Versions — ARM. https://en.wikichip.org/wiki/arm/versions ↩

  4. Wikipedia contributors. (n.d.). AArch64. Wikipedia. https://en.wikipedia.org/wiki/AArch64 ↩↩

  5. Wikipedia contributors. (n.d.). ARM Cortex-A. Wikipedia. https://en.wikipedia.org/wiki/ARM_Cortex-A ↩