Intel Publishes “X86-S” Specification For 64-bit Only Architecture


Intel quietly released a new whitepaper and specification for their proposal on “X86-S” as a 64-bit only x86 architecture. If their plans workout, in the years ahead we could see a revised 64-bit only x86 architecture.

Entitled “Envisioning a Simplified Intel Architecture”, Intel engineers lay the case for a 64-bit mode-only architecture. Intel is still said to be investigating the 64-bit mode-only architecture that they also refer to as “x86S”. Intel is hoping to solicit industry feedback while they continue to explore a 64-bit mode only ISA.

Intel X86-S specification

The X86-S mode would require booting CPUs directly into 64-bit mode and also allow for some fundamental changes like being able to switch to 5-level paging without leaving a paged mode.

Intel X86-S drops 32-bit software support

Among Intel’s expressed benefits for a 64-bit mode-only architecture is removing ring 1 and 2, dropping 16-bit addressing support, eliminating ring 3 I/O port accesses and the string port I/O, simplified segmentation model, and removing some unused operating system bits.

Under this proposal, those wanting to run legacy 32-bit operating systems would have to rely on virtualization. To further clarify, 32-bit x86 user-space software would continue to work on modern 64-bit operating systems with X86-S.

Those interested can see Intel’s documentation around the proposed 64-bit only architecture X86-S via

It’s still likely some years away before seeing this possible x86S/X86-S architecture for going 64-bit only but very interesting to see Intel beginning these moves for doing away with the legacy modes.