Streaming SIMD Extensions

In computing, Streaming SIMD Extensions (SSE) is a single instruction, multiple data (SIMD) instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in its Pentium III series of central processing units (CPUs) shortly after the appearance of Advanced Micro Devices (AMD's) 3DNow!.

SSE contains 70 new instructions (65 unique mnemonics[1] using 70 encodings), most of which work on single precision floating-point data.

The addition of integer support in SSE2 made MMX largely redundant, though further performance increases can be attained in some situations[when?]

During the Katmai project Intel sought to distinguish it from its earlier product line, particularly its flagship Pentium II.

AMD eventually added full support for SSE instructions, starting with its Athlon XP and Duron (Morgan core) processors.

This limitation reduces the effectiveness of pipelining, but the separate XMM registers do allow SIMD and scalar floating-point operations to be mixed without the performance hit from explicit MMX/floating-point mode switching.