Once upon the time and back to 2000, Intel brought to market NetBurst microarchitecture (http://en.wikipedia.org/
For years, PC programmers used x86 assembly to write performance-critical code. However, 32-bit PCs are being replaced with 64-bit ones, and the underlying assembly code has changed. This white paper is an introduction to x64 assembly.
For more complete information about compiler optimizations, see our Optimization Notice.