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Benchmarks reveal that AVX2+FMA code runs at only 2/3 the speed of SSE2-4.x code when emulated on Windows 11 ARM via Microsoft's Prism emulation layer. Testing 21 math operations on 64-bit doubles, AVX2 delivers a 2.7x speedup on native Intel hardware but a 33% slowdown under ARM emulation compared to the older SSE2-4.x baseline. The most likely cause is that ARM's 128-bit NEON registers force the emulator to split each 256-bit AVX2 operation into two halves, plus the Prism AVX2 emulation code is relatively new and may not be fully optimized. The practical recommendation: if your app targets Windows ARM, compile natively for ARM64 rather than relying on x86-64 v3 emulation for performance-critical code.

AVX2 is slower than SSE2-4.x under Windows ARM emulation