Exploring Intel’s x86S Architecture: The Future of Computing

The Evolution of Intel® Architecture and Power of Intel® 64

With its extensive history, Intel® Architecture has built a strong software ecosystem that encompasses a wide range of devices, including PCs, the cloud, mobile devices, embedded systems, supercomputers, and more. The Intel® 64 architecture has become the preeminent operating mode during the last 20 years. Microsoft’s decision to stop distributing the 32-bit version of their Windows 11 operating system serves as an example of this change.

Furthermore, non-UEFI64 operating systems are no longer natively supported by Intel firmware. These days, 32-bit applications may operate on 64-bit operating systems, which have replaced 16-bit operating systems as the industry norm.ng gadgets during the upcoming year.

Simplification in the Hardware and Software Ecosystem

In light of this evolution, Intel recognizes potential opportunities for simplification within its hardware and software ecosystem. Some legacy modes within the architecture serve limited purposes in modern operating systems, primarily aiding the transition to 64-bit mode. It raises the question of whether these seldom-used elements of the architecture could be removed to create a streamlined 64-bit mode-only architecture.

Intel’s Investigation into a 64-Bit Mode-Only Architecture (x86S)

This whitepaper unveils Intel’s exploration of architectural enhancements and modifications for a 64-bit mode-only architecture, tentatively named x86S (for simplification). Intel aims to gather feedback from the ecosystem while assessing the advantages of extending the ISA (Instruction Set Architecture) transition to a 64-bit mode-only solution. The proposed architecture seeks to eliminate certain legacy modes, resulting in a more straightforward and efficient design.

How a 64-Bit Mode-Only Architecture Would Work

Intel® 64 architecture designs begin in a state similar to the original 8086 architecture and require a series of code transitions to enter 64-bit mode. However, once in operation, these modes are rarely utilized by modern applications or operating systems. By transitioning to an exclusively 64-bit mode architecture, Intel would need to develop 64-bit equivalents for technologies that currently operate in real mode or protected mode. For instance:

• The booting process (SIPI) starts in real-address mode, which would require a 64-bit replacement in a mode-only architecture. A direct 64-bit reset state would eliminate the need for multiple stages of trampoline code to enter 64-bit operation.
• In the proposed architecture, switching to 5-level paging, which requires disabling paging in the current design, could be achieved without reverting to an unpaged legacy mode. This enhancement would streamline the operation and eliminate unnecessary transitions.

These modifications could be implemented through straightforward enhancements to the system architecture, primarily impacting the operating system.

Benefits of Transitioning to a 64-Bit Mode-Only Architecture

1. Utilizing the simplified segmentation model of 64-bit to support segmentation in 32-bit applications, aligning with existing practices in modern operating systems.
2. Eliminating unused ring 1 and 2, which are no longer utilized by modern software, as well as obsolete segmentation features like gates.
3. Removing support for 16-bit addressing, as it is no longer necessary in a 64-bit environment.
4. Eliminating support for ring 3 I/O port accesses.
5. Discontinuing string port I/O, which is associated with an outdated CPU-driven I/O model.
6. Limiting the use of the local interrupt controller (APIC) to X2APIC and removing legacy 8259 support.
7. Removing certain unused operating system mode bits, further simplifying the architecture.

Intel’s investigation into a 64-bit mode-only architecture presents an opportunity to streamline and simplify both the hardware and software ecosystem. By eliminating legacy modes and outdated features, Intel aims to enhance the efficiency and overall performance of its architecture while aligning with modern software practices. The industry feedback gathered during this exploration phase will contribute to shaping the future direction of Intel’s architecture.

Source: Intel Blog Post