Again, these ports are related to the internal hardware on your motherboard. There's a good overview of parallel port interfacing at http://www.beyondlogic.org/Originally Posted by barilan
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The parallel port contains 25 discrete pins. Some are transmit-only and some are receive-only.
Basically, data you are trying to send OUT of the computer goes to the base address (in many cases, 888) while data being received by the computer from an outside system is read by the computer at address + 1 (or sometimes, address +2. Hence 888 and 889.
In the case of a serial port, data is sent and received through the same port address.
Hope that helps.