From http://msdn.microsoft.com/en-us/library/7t5yh4fd(VS.80).aspx http://msdn.microsoft.com/en-us/library/7t5yh4fd(VS.80).aspx The optimizer will choose when a

From http://msdn.microsoft.com/en-us/library/7t5yh4fd(VS.80).aspx http://msdn.microsoft.com/en-us/library/7t5yh4fd(VS.80).aspx The optimizer will choose when and how to make use of the SSE and SSE2 instructions when /arch is specified. SSE and SSE2 instructions will be used for some scalar floating-point computations, when it is determined that it is faster to use the SSE/SSE2 instructions and registers rather than the x87 floating-point register stack. As a result, your code will actually use a mixture of both x87 and SSE/SSE2 for floating-point computations. Additionally, with /arch:SSE2, SSE2 instructions can be used for some 64-bit integer operations. In addition to using the SSE and SSE2 instructions, the compiler will also use other instructions that are present on the processor revisions that support SSE and SSE2. An example is the CMOV instruction that first appeared in the Pentium Pro revision of the Intel processors.