The Streaming SIMD Extensions 2 (SSE2) introduces new Single Instruction Multiple Data (SIMD) double-precision floating-point instructions and new SIMD integer instructions into the IA-32 Intel® architecture. The double-precision SIMD instructions extend functionality in a manner analogous to the single-precision instructions introduced with the Streaming SIMD Extensions (SSE). The 128-bit SIMD integer extensions are a full superset of the 64-bit integer SIMD instructions, with additional instructions to support more integer data types, conversion between integer and floating-point data types, and efficient operations between the caches and system memory. These instructions provide a means to accelerate operations typical of 3D graphics, real-time physics, spatial (3D) audio, video encoding/decoding, encryption, and scientific application. This application note discusses how to use the 128-bit SIMD integer instructions to implement multiplication where the size of the multiplicands is very large. We include examples of code that exploit the SSE2 instructions.