Linux to Drop Last MMX Code in 2027
Developers are removing MMX-optimized software RAID code from the Linux kernel, a change expected to ship with Linux 7.5.
Updated on Nov. 8, 2026 in Computers
Linux kernel developers are preparing to remove the last MMX-optimized code from the kernel, eliminating over 800 lines and replacing them with 12 lines. The change, a patch to the software RAID XOR code, is expected to arrive with Linux 7.5 in 2027.
Why it matters
Intel first introduced MMX Pentium chips in January 1997, and most MMX-optimized code was already removed from Linux about half a decade ago. The cleanup reflects that few users are expected to run modern kernels on Pentium MMX and Pentium II hardware.
The patch replaces more than 800 lines of MMX-optimized code with 12 lines in the software RAID XOR code. Software RAID will remain usable on Pentium MMX systems without the MMX fast path, though the performance impact of this change has not been detailed.
The players
Intel
Intel is the chipmaker that first introduced MMX Pentium processors in January 1997 and later developed SSE and SSE2 instructions.
AMD
AMD offered MMX CPUs and pioneered the 3DNow! instruction set that preceded Intel's SSE and SSE2.
The details
The MMX-optimized code remaining in Linux was located in the software RAID XOR code, and most other such code was removed from the operating system roughly five years ago. AMD, Centaur, Cyrix, Rise, and Transmeta also offered MMX CPUs, while AMD pioneered 3DNow! instructions that Intel's SSE and SSE2 later followed about a year afterward.
Timeline
January 1997: Intel introduces MMX Pentium chips.
Roughly half a decade ago: Most MMX-optimized code is removed from Linux.
2026: Few users are expected to run modern kernels on Pentium MMX and II chips.
2027: Linux 7.5 is expected to be released with the MMX code removed.
Roadmap
The removal caps a long arc that began with Intel's January 1997 MMX launch and continued through AMD's 3DNow! and Intel's SSE and SSE2 instruction sets. It marks the end of support for an instruction set that the kernel has been phasing out for about five years.
Users running Pentium MMX or Pentium II machines on the newest kernels will lose the MMX fast path for software RAID, though RAID remains functional. Most people running current hardware will see no practical change.
The takeaway
Hardware-specific optimizations tend to be retired once the hardware itself falls out of common use, keeping kernels lean for current systems. Users on legacy Pentium hardware should plan to stay on older kernels if they need the fastest RAID performance.
What happens next
Linux 7.5 is expected to ship in 2027 with the MMX code removed.
Further reading
For more on how processor features shape operating system design, explore Computers coverage.
Source note: This article includes information reported by Tom's Hardware.
