Simpler x86 Coming Soon

Intel’s proposed x86-S instruction set removes several legacy features, simplifying CPU designs but breaking compatibility with some old software. We expect it to debut in processors in 2025.
Linley Gwennap
Linley Gwennap

For four decades, Intel has carefully maintained compatibility with old operating systems and software, in case someone wants to run MS-DOS software on a brand-new PC (assuming one could figure out where to insert the floppy disk). The company has decided to finally break this compatibility, dropping several legacy features in its upcoming x86-S instruction set. Although presented as a “proposal” with no specific deployment date, the changes are already being designed into an Intel CPU that we expect to enter production within two years.

By eliminating 16-bit and 32-bit protected modes, x86-S will simplify CPU design and testing. Modern operating systems run in 64-bit mode; the new instruction set eliminates features used by 32-bit operating systems, but 32-bit applications can still run natively in 32-bit user mode. Ancient 16-bit applications are already supported in emulation at speeds far faster than they ever ran on hardware.

We believe the x86-S disclosure is related to an internal Intel project, sometimes called Royal, to develop a “from-scratch” CPU, its first in more than a decade. Designing completely new instruction decoders, execution units, and TLBs is an ideal opportunity to make major changes in the instruction set. We expect the new CPU to debut in the Lunar Lake PC processor in 2025. The recent x86-S disclosure leaves time to make minor changes before that CPU design is frozen later this year. The new instruction set will then appear in all subsequent CPU cores.

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