According to the University of Mexico, serial ports transmit data one bit at a time, whereas parallel ports transmit 8 bits of data at a time. The location of the port depends on the age and type of the device.
On older computers, serial ports are connected to a keyboard, modem or mouse; a parallel port is faster and is connected the printer. Newer computers use a wide range of ports to connect various hardware devices. The Universal Serial Bus, or USB port, is the most commonly used to connect devices such as an external drive, keyboard, scanner, mouse, printer or audio. Other commonly used ports are FireWire, Ethernet, PCMCIA, Audio Ports and SCSI.