In a move to streamline its software and hardware ecosystem, Intel has released a whitepaper detailing its investigation into a 64-bit mode-only architecture referred to as x86S (for simplification). The proposal aims to remove certain legacy modes that have limited utility in modern operating systems, presenting an opportunity for simplification and increased efficiency.
The long-standing dominance of Intel Architecture has fostered a robust software ecosystem across various platforms, ranging from PCs to cloud services, mobile devices, embedded systems, and supercomputers. However, as technology continues to evolve, Intel recognizes the need to adapt and optimize its architecture for current and future demands.
The whitepaper highlights the architectural enhancements and modifications that Intel is exploring for a 64-bit mode-only architecture. The company seeks feedback from the ecosystem as it evaluates the potential benefits and impacts of extending the Instruction Set Architecture (ISA) transition to a 64-bit mode-only solution.
Current Landscape
Currently, Intel’s 64-bit architecture designs initialize in a state similar to the original 8086 processor and require a series of code transitions to enter 64-bit mode. However, these modes are rarely utilized by modern applications or operating systems. With the proposed 64-bit mode-only architecture, Intel aims to eliminate the need for these unused elements, simplifying the overall architecture.
The transition to a 64-bit mode-only architecture would require 64-bit equivalents for technologies currently running in real mode or protected mode. For instance, booting CPUs (SIPI) currently starts in real-address mode and would require a 64-bit replacement. By directly entering a 64-bit reset state, the proposed architecture eliminates the need for multiple stages of trampoline code to initiate 64-bit operation.
Moreover, the proposed architecture facilitates the use of 5-level pages without disabling paging or reverting to unpaged legacy mode. This advancement offers more efficient memory management, eliminating unnecessary transitions and improving overall system performance.
The benefits of a 64-bit mode-only architecture are significant. Removing older appendages of the architecture reduces complexity in both software and hardware. By aligning with modern software deployment practices, the proposal suggests using the simplified segmentation model of 64-bit for segmentation support in 32-bit applications, matching the approach already employed by contemporary operating systems.
Moving to 64-Bit Only
The proposal also suggests removing unused ring 1 and 2, obsolete segmentation features like gates, 16-bit addressing support, and ring 3 I/O port accesses. Additionally, string port I/O, which supports an outdated CPU-driven I/O model, could be eliminated. Furthermore, the proposal recommends limiting the use of the local interrupt controller (APIC) to X2APIC and phasing out legacy 8259 support. Removing some unused operating system mode bits further simplifies the architecture.
While the transition to a 64-bit mode-only architecture does not explicitly aim to support legacy operating systems, the matured Intel architecture software ecosystem provides virtualization solutions that can emulate features necessary to boot these older systems. By utilizing virtualization hardware (VMX), a virtualization-based software solution could bridge the gap and enable legacy operating systems to run on top of the 64-bit mode-only architecture.
Intel invites feedback from stakeholders and the broader ecosystem on the architectural proposal to evaluate potential impacts to software. Interested parties can provide their input by emailing Intel directly.
As Intel continues to explore innovative solutions, this proposal signifies the company’s commitment to optimizing its architecture for modern computing needs. The transition to a 64-bit mode-only architecture holds the promise of simplifying software and hardware ecosystems, ultimately delivering improved performance, efficiency, and compatibility in the ever-evolving technology landscape.
The full whitepaper can be viewed here.
