serial ports:
-have small cables. This means there is little electrical interference. This allows them to be up to 300m long.
-Bidirectional, meaning the device can transfer, as well as receive data.
-They are used for mice, keyboards and external modems.
parallel ports:
-Made up of 25 wires that allow data to be transferred simultaneously.
-Limited to short distances or else data may be corrupt.
-Able to send+receive large amounts of data.
-Used in printers, scanners, zip drives.
Hope that helps