Linked by Thom Holwerda on Fri 5th Apr 2013 16:04 UTC
"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. No prior knowledge of x86 code is needed, although it makes the transition easier."