Compare parallel port and serial port?

A serial port is a 9 pin, RS-232 connection usually used for Terminal connections and older modems as well as some mice and older keyboards for example.

It has lost much of it's popularity and is uncommon on modern computers, usually must be emulated via USB or another port. Usually it's low speed with a asynchronous connection.

A parallel port is usually a 25 pin connection used primarily for printers, some times external devices such as Hard drives or CD-ROM drives, even scanners and modems. It is able to send more then one bit at a time. It is also becoming more obsolete and is less and less common on modern computers.

Hope that helps.