Each video card has a different limit. If you develop against GLSL, you have the limit of whatever videocard you're using, which is substantially different fro

Each video card has a different limit. If you develop against GLSL, you have the limit of whatever videocard you're using, which is substantially different from what DX would have you believe its limit is. GPUs are capable of more than what Microsoft would have you believe they're capable of. The limits that you're referring to are artificial, because Microsoft mandates that if a pixel shader has more than N instructions then it shouldn't be allowed to compile, regardless of what the videocard is actually capable of doing. It's confusing, and the reason they decided to do it that way was for compatibility across a wide variety of hardware.