What is a Serial / Parallel controller card?
A serial or parallel controller card is an add-in board that enables access to more ports than are available onboard the motherboard.
What to look for in a Serial / Parallel card?
Primarily you should be looking for the number of ports available and if they are of the correct type for your needs. Many controller cards will also feature internal ports or headers to enable the connection of devices from within the PC case. The brand of chip used on the controller can be important when purchasing as performance can vary between different models.