# Linux 7.5 removes final Intel MMX optimizations, dropping 800 lines of Pentium-era code

> **Key takeaway:** The Linux kernel is removing its last MMX-optimized software RAID XOR routines, replacing over 800 lines of 1997-era Pentium code with 12 lines of modern implementation in Linux 7.5.

**Published:** 2026-11-08T14:40:00+00:00 
**Source:** Tom's Hardware 
**Category:** open-hardware 
**Canonical URL:** https://fosswire.org/news/linux-75-removes-final-intel-mmx-optimizations-dropping-800-.html 

## Summary
A patch queued for Linux 7.5 will eliminate the final remnants of Intel MMX instruction set optimizations from the kernel, specifically removing MMX-accelerated XOR routines from the software RAID subsystem. Intel introduced MMX in January 1997 with its Pentium MMX processors, and the instructions were later adopted across the x86 industry by AMD, Centaur, Cyrix, Rise, and Transmeta. Most MMX-optimized kernel code was already removed approximately five years ago when MMX-based memory management routines were deleted; this change completes the cleanup by targeting the software RAID fast path.

The patch reduces the relevant codebase from over 800 lines to just 12, representing a significant maintenance win. Users attempting to run modern Linux kernels on genuine Pentium MMX or Pentium II hardware will retain software RAID functionality but without the MMX-optimized performance path. The change reflects the kernel's ongoing evolution away from obsolete ISA extensions toward cleaner, more maintainable code that assumes SSE2 or newer vector capabilities on all supported x86 hardware.

## What changes in the RAID XOR MMX removal
- **Software RAID XOR subsystem:** The final MMX-optimized code path resides in the kernel's software RAID XOR calculation routines, which use parity computations for RAID 4, 5, and 6 redundancy.
- **Code reduction:** The patch removes over 800 lines of MMX assembly and C code, replacing them with approximately 12 lines of implementation, dramatically shrinking the maintenance surface.
- **Historical context:** Most MMX kernel optimizations were already purged roughly five years prior when MMX-enhanced memory management code was removed, leaving only this RAID XOR fast path.
- **Functional preservation:** Software RAID continues to operate on affected legacy hardware, but falls back to non-MMX generic implementations rather than the removed optimized path.
- **ISA succession:** MMX was succeeded by AMD's 3DNow! and Intel's SSE/SSE2; modern x86 Linux effectively assumes SSE2 baseline, making MMX-only optimizations redundant.

## Why it matters
This cleanup eliminates a rarely-tested legacy code path that has accumulated technical debt across nearly three decades, reducing the attack surface and maintenance burden for distribution kernel maintainers who backport RAID fixes. For the broader open-source ecosystem, it signals the Linux kernel's continued willingness to deprecate obsolete hardware optimizations when the affected systems are no longer viable targets for modern kernels, freeing developer attention for contemporary architectures including RISC-V and ARM64 server platforms.