Peripheral Device Connections

A peripheral device is a device that connects through an external port to your computer. The following connection types are common:


PS/2 connectors are 6-pin mini-din connectors. Keyboard and mouse are common devices that use PS/2 connections. The correct device must be connected to the correct port; a specific port is used for the keyboard, with a different port for the mouse. Devices can be auto-detected, but must be plugged in when the computer starts up.


USB is a serial interface that supports low- and high-speed devices.  USB supports almost any kind of peripheral device, including keyboards, mice, scanners, digital cameras, printers, and storage devices. Note: USB ports on video cameras are typically used for transferring still images to the computer.

USB supports Plug-and-Play and hot swapping (adding and removing devices without rebooting--also known as hot plugging).

To install a USB device, you should typically install the software driver before attaching the device. When you plug in the device, it will be automatically detected and configured.

Edit the BIOS settings to disable onboard USB ports or configure the USB mode for either version 1.1 or 2.0.

All devices connected together share computer resources (IRQs, I/O addresses).


Firewire is a serial interface. Common Firewire devices include digital video cameras and recorders, hard drives, and network adapters. Firewire ports on video cameras are typically used for transferring digital video. Firewire supports Plug-and-Play and hot-swapping


Serial devices transmit data one bit at a time on a single cable. Serial devices use COM ports for system resources. Remember that COM ports 1 and 3, and ports 2 and 4 are shared. If you install a serial device on both COM 1 and COM 3, the devices might cause a resource sharing problem.

The most common serial device is a modem. Some specialized printers might also use a serial interface. Many newer computers no longer include a serial port. To add serial ports to a computer, install an adapter card.


Parallel devices transmit multiple bits at a time over multiple wires. Parallel devices use LPT ports for resources. Common parallel devices include printers and scanners.

Parallel communication uses one of the following standards (or modes):

  • Standard Parallel Port (SPP)
  • Enhanced Parallel Port (EPP)
  • Extended Capabilities Port (ECP)

Both EPP and ECP support bi-directional communication. ECP supports DMA. Edit the CMOS settings to configure the parallel modes supported.


PC Cards are expansion slots in laptop and portable devices. PC Cards can be used by devices like modems, network cards for wired or wireless networks, CD-ROMs, sound cards, SCSI host adapters, IEEE 1394 controllers, USB controllers, and others.

PCI Express (ExpressCard)

PCI Express (ExpressCard) is replacing PC Card for laptop expansion devices. ExpressCard slots connect directly to the PCIe or USB bus. Cards use either PCI Express or USB 2.0 standards (the slot supports both).

ExpressCards can be used for all types of devices, similar to PCMCIA. An ExpressCard can even be used for a graphics card to attach an external monitor. Many newer laptops have ExpressCard slots but not PCMCIA slots. Some laptops have both, while some have neither (assuming that all external devices will connect through the USB ports).

Many of these ports and interfaces are included as part of the motherboard faceplate connectors. To add support for additional ports, do one of the following:

  • If the motherboard includes header connections for the ports, connect the cables and ports to the system case or an expansion slot.
  • Add an expansion card to provide the necessary ports.