Why I Wrote This Blog
While exploring which toolchain to use for compiling the Linux kernel for the BeagleBone Black (ARM Processor based) , I came across several terms that seemed similar — ARMv7 architecture, Cortex-A8 microarchitecture, and ARM core.
At first, they looked like synonyms. But as I dug deeper, I realized they each refer to something entirely different.
That’s when I thought — why not write a crisp and clear explanation that helps embedded professionals understand these terms once and for all?
🔍 What Is ARM?
ARM stands for Acorn RISC Machine, later renamed Advanced RISC Machine.
Founded in 1990, Arm Holdings designs the architecture and intellectual property (IP) behind most modern embedded and mobile processors. Interestingly, Arm does not manufacture chips — instead, it licenses its architecture and cores to companies like NXP, STMicroelectronics, Broadcom, Qualcomm, and Apple.
This licensing model allows manufacturers to integrate ARM cores into their own SoCs (System on Chips), customizing them for performance, power, and cost.
In simple terms:
👉 Arm designs the brain
👉 Chipmakers build the body around it
This is why ARM processors power everything from microcontrollers (MCUs) to high-end smartphones.
🧩 The Three Layers of ARM Processor
To understand the ARM ecosystem, you must clearly distinguish between three terms:
- Architecture
- Microarchitecture
- Core
Each has a different meaning and role.
1️⃣ ARM Processor Architecture
The architecture defines the Instruction Set Architecture (ISA) — the “language” that tells the processor what instructions it can execute and how.
It defines:
- The instruction set (ARM, Thumb, Thumb-2, AArch64)
- The register model
- Exception and privilege levels
- Memory model
- Data types and addressing modes
Some of the popular ARM architectures include:
| Architecture | Key Feature | Example Devices |
|---|---|---|
| ARMv4 | Early RISC base | ARM9 series |
| ARMv5 | Jazelle (Java support) | ARM926EJ-S |
| ARMv6 | SIMD extensions | Raspberry Pi (original) |
| ARMv7 | Thumb-2, NEON | BeagleBone Black, Cortex-A8/A9 |
| ARMv8 | 64-bit support | Raspberry Pi 3, ARM Cortex-A53 |
| ARMv9 | Enhanced AI and security | Newer mobile SoCs |
When you read ARMv7 architecture, it refers to the design specification, not a specific chip or core.
2️⃣ ARM Microarchitecture
The microarchitecture defines how the architecture is implemented — the internal design details such as:
- Pipeline depth
- Cache hierarchy
- Branch prediction
- Execution units
- Power management
Arm develops different microarchitectures for various use cases — performance, real-time, or power efficiency.
| Microarchitecture | Based On | Target Segment |
|---|---|---|
| Cortex-A8 | ARMv7-A | Application processors |
| Cortex-R5 | ARMv7-R | Real-time systems |
| Cortex-M4 | ARMv7-M | Microcontrollers |
Think of it like this: multiple car models (Cortex-A8, R5, M4) can all run on the same fuel type (ARMv7 architecture), but they’re tuned for different terrains.
3️⃣ ARM Core
A core is the actual hardware implementation of a specific microarchitecture.
For example:
- The Cortex-A8 core implements the ARMv7-A architecture using the Cortex-A8 microarchitecture.
- In BeagleBone Black, the TI AM335x SoC contains a single Cortex-A8 core.
So, to summarize:
Architecture → defines what to build
Microarchitecture → defines how to build it
Core → is the final built product
⚙️ Example: BeagleBone Black
Let’s take a real example to make it concrete:
| Term | Example |
|---|---|
| Architecture | ARMv7-A |
| Microarchitecture | Cortex-A8 |
| Core | Cortex-A8 core inside TI AM335x SoC |
When you compile your Linux kernel using a cross-toolchain like arm-linux-gnueabihf-gcc, it’s targeting the ARMv7-A architecture.
🚀 Why It Matters for Embedded Developers
Understanding these distinctions helps you:
✅ Choose the correct cross-compiler and toolchain flags (-march, -mcpu, -mtune)
✅ Interpret datasheets and TRMs more confidently
✅ Configure the Linux kernel correctly for your board
✅ Optimize your builds for performance and compatibility
This foundational clarity separates developers who “run” ARM systems from those who truly understand them.
🚀 Build Your Linux Foundations
If you want to go from user-space to kernel-level mastery:
- Linux Rapid Mastery → Learn Linux Fundamentals, Applications, Driver Basics & Kernel Internals
👉 https://embitude.in/lrm
Join the community of passionate embedded engineers:
👉 https://embitudeinfotech.graphy.com/s/community
🧭 Key Takeaways
- Architecture defines what instructions exist.
- Microarchitecture defines how they’re executed.
- Core is the hardware realization.
- Understanding these helps you build, debug, and optimize efficiently.