That is for all intel and amd processors which support SSE. This is practically all the PC market today. But it isn't portable to consoles (you have to convert the code to their instruction sets).

Wouldn't it be nice if the original post would have specified which platforms you are targeting, about how many 4x4 systems of linear equations you will be solving per second, whether you are using floats or doubles, what potential solutions you were already aware of, what you had tried, how slow that was...