Streaming SIMD Extensions

SSE is a SIMD instruction set designed by Intel, introduced in their Pentium III series processors.

Intel was generally disappointed with their earlier SIMD effort, MMX, and were looking to offer new functionality to separate the new Pentium III from their earlier product line. MMX had two main problems: it re-used existing floating point registers making the CPU unable to work on both floating point and SIMD data at the same time, and it worked on only two 32-bit integers at once.

SSE, originally known as KNI for Katmi New Instructions (Katmi was the code name for the Pentium III) added eight 128-bit registers that were divided up into four 32-bit floating point numbers. Performance was much improved, with no downside, and SSE has seen better adoption than MMX.