Hello Waruna,
it will depend on your computer,
there is a knowledge base article with some benchmark results that show that you can reach almost 1kHz update rate for a port if you are using a high performance PC. Nevertheless, the digital lines on the device are software timed and meant to be static - that means they are not designed for fast switching operations - that is why there is a limit in speed.
If you would like to do a faster and / or hardwaretimed operation, you should think about using a M-Series board.
Ingo Schumacher
Systems Engineering Manager CEERNational Instruments Germany