The Shift from x86 to ARM in Laptops and Desktops: What's Driving the Trend?

In recent years, the tech industry has been witnessing a significant shift: major operating systems like Windows and Linux, traditionally designed for x86 architectures (Intel and AMD), are now running on ARM-based systems. While ARM has long dominated mobile and embedded devices, ARM-powered laptops and desktops are now becoming mainstream, running popular OSs effortlessly.

So, why is this happening? What makes ARM so attractive, and why are manufacturers moving towards it? The answer lies in the fundamental differences between ARM and x86 architectures, particularly how they implement their Instruction Set Architectures (ISAs).

This article, inspired by insights from Casey Muratori’s podcast on ThePrimeTime YouTube channel , digs deeper into these differences and explores the key reasons behind ARM’s rise in the desktop and laptop space.

RISC vs. CISC: The Key to Understanding the Shift

At the heart of this transition is the architectural difference between RISC (Reduced Instruction Set Computing) and CISC (Complex Instruction Set Computing). ARM is based on RISC, while Intel and AMD processors use the CISC approach. While it's common knowledge that RISC cores are more power-efficient, understanding why requires a closer look at how these architectures operate at the binary level.

In his podcast, Casey Muratori uses tools like Godbolt to demonstrate how the same C code translates into assembly instructions for both ARM (RISC) and Intel x86 (CISC). The differences in the resulting assembly code illustrate why ARM is generally more power-efficient.

Assembly Code Comparison: ARM vs. x86

When compiling C code for ARM, the resulting assembly language is uniform and predictable. Each instruction is 4 bytes (or 8 bytes in 64-bit mode), making the execution simple and efficient. ARM’s RISC philosophy focuses on simplicity and efficiency—each instruction is atomic and performs a single operation, allowing the processor to execute them quickly without much overhead.

On the other hand, compiling the same C code for x86 results in assembly instructions that vary greatly in size. Some instructions might be 2 bytes, others 4, 8, or even 16 bytes long. CISC instructions are designed to be complex, often doing more in a single instruction. However, this complexity introduces hidden overhead and inefficiency.

The Hidden Complexity of x86 Micro-Operations

One of the key points that Casey Muratori emphasizes is the complexity hidden within CISC instructions. While a CISC instruction may appear to perform a complex task in one step, it’s internally broken down into multiple smaller micro-operations (or micro-ops) within the processor.

For example, a single CISC instruction can break down into several micro-ops, which are then executed sequentially by the CPU. This is essentially RISC-like behavior hidden within the CISC architecture. The downside? This breakdown requires extra clock cycles and more power to decode and execute.

In contrast, ARM’s RISC architecture executes each instruction directly without breaking it down into micro-ops. This results in lower power consumption and greater efficiency, making ARM processors more suitable for mobile and battery-powered devices.

Look at the examples below, where its shows clearly how Intel x86-64 GCC compiler vs AMR 64 GCC compiler generates code for the same ‘C’ code and how the various assembly level instructions differ in byte size and binary machine code.

Instruction Decoding: The Power Drain in x86

The decode phase of a processor’s instruction pipeline is one area where ARM has a clear advantage over x86. In Intel's x86 architecture, the CPU must parse each instruction ahead of time to figure out where the next instruction starts, since x86 instructions can vary in length. This process takes additional clock cycles, increasing power consumption and inefficiency.

ARM's RISC design avoids this problem entirely. Since ARM instructions are always the same size (4 or 8 bytes), the CPU always knows where the next instruction begins, eliminating the need for extra parsing in the decode phase. This design further contributes to ARM's power efficiency.

Why Does This Matter for Laptops and Desktops?

For decades, x86-based processors were the go-to for desktops and laptops because they delivered the raw performance needed for heavy workloads like gaming, video editing, and programming. However, the landscape is changing. Energy efficiency is becoming just as important as raw power in modern computing, especially with the rise of mobile and portable devices.

ARM processors strike a balance between performance and power efficiency, making them ideal for devices that need to be powerful yet energy-conscious. By simplifying the architecture and reducing overhead, ARM processors consume less power, generate less heat, and still provide the performance required for most mainstream applications.

The Rise of ARM in the Desktop World

The shift from x86 to ARM in laptops and desktops is more than just a passing trend—it’s a reflection of the evolving needs of the computing world. ARM’s RISC architecture offers advantages that x86’s CISC approach struggles to match, especially in terms of power efficiency and simplicity.

As we look toward a future where energy-efficient computing is critical, ARM’s role will only grow stronger. While x86 processors still have their place in high-performance computing, ARM is becoming the architecture of choice for manufacturers and developers alike, reshaping the landscape of laptops and desktops.

In conclusion, ARM is no longer just the go-to architecture for mobile devices—it's transforming the desktop and laptop market, delivering power efficiency and performance that x86 struggles to match. As manufacturers embrace ARM for mainstream computing, we're witnessing a new era in tech.

The real question is, how long until ARM dominates the desktop space too? The shift is here, and the future is ARM.