It's not just that the compiled code isn't as efficient as it's supposed to be. It is also quite simply that the P4 has a weak FPU, regardless of the code. Now, if the P4 is the only CPU your code works on, that doesn't have to be that big of a problem. Instead of using the FPU you can often use ISSE2 instructions. But that poses programmers with 2 major problems: 1) You have to manually optimize your program for the P4 instructions and you can't do it in a high level language. That means a lot of extra time, money, expertise is needed for something which was and is not needed for all other processors. 2) You have to make a program that uses different code for the P4 and other x86 processors. That means more time and money is needed. It also means that the program becomes more complex, more difficult to maintain and will have more bugs. Lots of companies don't even want to write for multiple operating systems. (Win32 and MacOS) let alone, that they want to write for multiple CPUs. Whereever possible they will write one piece of code in a high level language and will let the compiler make a Win32 and a Mac version. If a compiler is able to make some optimalizations all by itself that is fine. (But again: that is not enough for the P4)