"Getting the correct behavior in the case of parallel components (note that this applies even to single-core systems, since dedicated hardware constructs can ra

"Getting the correct behavior in the case of parallel components (note that this applies even to single-core systems, since dedicated hardware constructs can race with the CPU) is particularly tricky." Heck, even if you emulate the documented performance perfectly, you can still suffer regression behavior if the existing program just happens to rely on misbehavior of the original hardware due to less tolerant exception handling, stricter memory alignment protections, etc. in the later deployment environment. I've seen this a lot in memory misuse / misalignment when porting between various UNIX implementations. If your development environment just happens to forgive a lot of sloppiness (cough Solaris cough), misbehavior may only show up later on other platforms.