What are the delays in reading/writing the parallel and serial port?

I've heard that there are are delays of several milliseconds when reading from or writing to the parallel port using the DAQ toolbox. Also heard that the delay increases with increasing active pins. However I cannot any documentation or reported online information to confirm this or give specific values.

Has anyone measured this? Is there a way around it (in Psychtoolbox for example)? Does this apply to the serial port also?