Intel has announced it will not proceed with X86S, an experimental instruction set architecture that aims to simplify its processor design by removing legacy support for older 32-bit and 16-bit operating modes. The decision comes after gathering feedback from the technology ecosystem on a draft specification that was released for evaluation. The x86, and its 64-bit x86-64 we use today, is a giant cluster of specifications that contains so many instructions rarely anyone can say with precision how many are there. All of this stems from the era of original 8086 processor, which has its own 16-bit instructions. Later on we transitioned to 32, then 64-bit systems with all have brought their own specific instructions. Adding support for processing of vector, matrix, and other data types has increased the ISA specification so much that no one outside a few select engineers at Intel (and AMD) understands in full. From that x86S idea was born to solve the issue of supporting legacy systems and legacy code, and moving on to the x86S ISA, where "S" stands for simplified.

The X86S proposal included several notable modifications, such as eliminating support for rings 1 and 2 in the processor's protection model, removing 16-bit addressing capabilities, and discontinuing legacy interrupt controller support. These changes would have potentially reduced hardware complexity and modernized the platform's architecture. A key feature of the proposed design was a simplified boot process that would have allowed processors to start directly in 64-bit mode, eliminating the current requirement for systems to boot through various legacy modes before reaching 64-bit operation. The architecture also promised improvements in handling modern features like 5-level paging. "Intel will continue to maintain its longstanding commitment to software compatibility," the company stated in the official document on its website, acknowledging that the x86S dream is over.

AVX-512 was proposed by Intel more than a decade ago—in 2013 to be precise. A decade later, the implementation of this instruction set on CPU cores remains wildly spotty—Intel implemented it first on an HPC accelerator, then its Xeon server processors, then its client processors, before realizing that hardware hasn't caught up with the technology to execute AVX-512 instructions in an energy-efficient manner, before deprecating it on the client. AMD implemented it just a couple of years ago with Zen 4 with a dual-pumped 256-bit FPU on 5 nm, before finally implementing a true 512-bit FPU on 4 nm. AVX-512 is a microcosm of what's wrong with the x86 ecosystem.

There are only two x86 CPU core vendors, the IP owner Intel, and its only surviving licensee capable of contemporary CPU cores, AMD. Any new additions to the ISA introduced by either of the two have to go through the grind of their duopolistic competition before software vendors could assume that there's a uniform install base to implement something new. x86 is a net-loser of this, and Arm is a net-winner. Arm Holdings makes no hardware of its own, except continuously developing the Arm machine architecture, and a first-party set of reference-design CPU cores that any licensee can implement. Arm's great march began with tiny embedded devices, before its explosion into client computing with smartphone SoCs. There are now Arm-based server processors, and the architecture is making inroads to the last market that x86 holds sway over—the PC. Apple's M-series processors compete with all segments of PC processors—right from the 7 W class, to the HEDT/workstation class. Qualcomm entered this space with its Snapdragon Elite family, and now Dell believes NVIDIA will take a swing at client processors in 2025. Then there's RISC-V. Intel finally did something it should have done two decades ago—set up a multi-brand Ecosystem Advisory Group. Here's what it is, and more importantly, what it's not.

Intel has released version 1.2 of its X86S architecture specification. The X86S project, first announced last year, aims to modernize the x86 architecture that has been the heart of PCs since the late 1970s. Over the decades, Intel and AMD have continually expanded x86's capabilities, resulting in a complex instruction set that Intel now sees as partially outdated. The latest specification primarily focuses on removing legacy features, particularly 16-bit and 32-bit support. This radical departure from x86's long-standing commitment to backward compatibility aligns with the simplification of x86. While the specification does mention a "32-bit compatibility mode," we are yet to how would 32-bit apps run. This ambiguity raises questions about how X86S might handle existing 32-bit applications, which, despite declining relevance, still play a role in many computing environments.

The potential transition to X86S comes at a time when the industry is already moving away from 32-bit support. However, the proposed changes are subject to controversy. The x86 architecture's strength has long been its extensive legacy support, allowing older software to run on modern hardware. A move to X86S could disrupt this ecosystem, particularly for users relying on older applications. Furthermore, introducing X86S raises questions about the future relationship between Intel and AMD, the two primary x86 CPU designers. While Intel leads the initiative, AMD's role in the potential transition remains uncertain, given its significant contributions to the current x86-64 standard.

Intel has published a highly involved and extensive whitepaper on the topic of streamlining its CPU architectures, most notably by focusing on a purely 64-bit specification, and consequently dropping legacy 32-bit operating modes (as well as 16-bit!). Team Blue's key proposal states: "This whitepaper details the architectural enhancements and modifications that Intel is currently investigating for a 64-bit mode-only architecture referred to as x86S (for simplification). Intel is publishing this paper to solicit feedback from the ecosystem while exploring the benefits of extending the ISA transition to a 64-bit mode-only solution."

The paper provides a bit of background context: "Since its introduction over 20 years ago, the Intel 64 architecture became the dominant operating mode. As an example of this evolution, Microsoft stopped shipping the 32-bit version of their Windows 11 operating system. Intel firmware no longer supports non UEFI64 operating systems natively. 64-bit operating systems are the de facto standard today. They retain the ability to run 32-bit applications but have stopped supporting 16-bit applications natively. With this evolution, Intel believes there are opportunities for simplification in our hardware and software ecosystem."