I/O ports are the physical connections that components use to connect to the motherboard. A keyboard or mouse are considered input devices while a printer or monitor are considered output devices. A modem or NIC are considered to be both input and output.

Parallel Port

• 25-pin female D-shell (DB)
• Color coded as magenta
• Uses Line Print Terminal (LPT) interface
• 8-bit wide data bus
• Up to 2 MBps data transfer
• Cable length up to 10 meters (Approx. 30 feet)
• Bi-directional communication
• Adheres to IEEE 1284 standard
• Printer cables typically have a 36-pin Centronics connector at one end
• Was commonly used for printers and external drives but now largely replaced by USB
• Has different modes: Nibble, Compatibility, BYTE, EPP, ECP
• Can be daisy-chained with up to 8 devices

The IEEE 1284 specifies a daisy chaining standard that allows up to eight devices to be connected to a single parallel port.

• Enhanced parallel port (EPP) is an IEEE 1284 mode that specifies a half-duplex, bi-directional standard used by non-printing devices to send large amounts of data to the host

• Extended capabilities port (ECP) is an IEEE 1284 mode that specifies a half-duplex, bi-directional standard that allows greater transfer speeds and compression. ECP has a DMA channel

Serial

• 9-pin and 25-pin male D-shell (DB)
• Cable length up to 15.25 meters (Approx. 50 feet)
• Up to 115,200 bps data transfer serially
• Was commonly used for external modems but now largely replaced by USB
• Commonly called Communication (COM) ports
• Uses start and stop bits (Asynchronous)
• Adheres to RS-232 standard
• Asynchronous and Synchronous
• Null modem and RS-232 (regular)
• Null modem cables have pin in/out configurations that are opposite at each end and connect directly to another computer for communication

PS/2

• 6-pin female Mini-DIN connector
• Serial bus technology
• Designated for keyboard and mouse
• Color coded: purple is the keyboard port and green is the mouse port
• Not hot-pluggable
• Replaced by USB

USB

• A, B, 4 to 5-pin Mini connectors
• Serial bus technology
• Controller supports up to 127 devices
• Self-powered and can supplies 5V at up to 500mA
• Cable lengths range from 3 meters (USB 1.0) to 5 meters (USB 1.1/2.0)
• Powered USB hubs can extend cable range up to 30 meters
• 1.5 Mbps (USB 1.0), 12 Mbps (USB 1.1), and 480 Mbps (USB 2.0) data transfer
• Hot-pluggable

Firewire/IEEE 1394

• 6 and 9-pin connectors
• Serial bus technology
• Controller supports up to 63 devices
• Cable length up to 4.5 meters (IEEE 1394A) and 100 meters (IEEE 1394B)
• Standard data throughputs are 400 Mbps (IEEE 1394A) and 800 Mbps (IEEE 1394B)
• Firewire is a trademarked name, therefore Firewire is known by it's specification on PCs, IEEE 1394
• Self-powered with about 25-30V
• Hot-pluggable

Video Graphics Array (VGA)

• 15-pin D-subminiature (DE) connector
• Still found on video cards
• Cable length varies
• Analog signal

Digital Visual Interface (DVI)

• Up to 25-pin female connector
• Both Analog and Digital modes
• DVI-A has an analog output signal; DVI-I supports both analog and digital output signals; DVI-D has only a digital output signal.
• Cable length varies

Audio Ports

• 3.5mm Tip/Ring/Sleeve (TRS) plugs
• Almost universally known as audio jacks
• Color code standard not always honored