Expansion Bus Types

Expansion slots provide a connection for a number of devices and functions. To add features to your computer, you can typically add a peripheral card to an existing bus slot. The following list arecommon expansion buses in a PC system:

Peripheral Component Interconnect (PCI)

PCI supports a 32- or 64-bit I/O bus providing compatibility with both 486 and Pentium machines.

  • This bus is processor independent (the CPU and the PCI bus can process concurrently).
  • PCI is plug-and-play, meaning that newly installed devices can be detected and configured automatically.
  • PCI buses are most commonly used for devices such as sound cards, modems, network cards, and storage device controllers.

PCI slots are typically white.

Mini-PCI

Small form factor computers, such as laptops or micro-ATX systems, might include a mini-PCI slot. Mini-PCI devices are small cards with either 100- or 124-pins. A typical use for a mini-PCI slot is to add internal cards (such as wireless cards) to laptops.

Peripheral Component Interconnect Express (PCIe)

PCI Express (PCIe) is a next generation I/O bus architecture. Rather than a shared bus, each PCIe slot links to a switch which prioritizes and routes data through a point-to-point dedicated connection and provides a serial full-duplex method of transmission.

  • Basic PCIe provides one lane for transmission (x1), at a transfer rate of 2.5 Gbps. It can also provide multiple transmission lanes (x2, x4, x8, x16, x32).
  • In addition to greatly increased speed, PCIe offers higher quality service.
  • PCIe is backwards compatible and allows legacy PCI technology to be run in the same system (i.e. you can have both PCIe and PCI buses in the same system).
  • PCIe buses are most commonly used for video cards in modern computer systems, although nearly any other device can be designed for a PCIe slot.

Accelerated Graphics Port (AGP)

AGP is similar to PCI, but designed specifically for graphics support. Motherboards that provide AGP support have a single AGP slot. AGP is commonly used for video cards in modern computer systems, but is being replaced by PCIe. AGP slots are typically brown.

Audio Model Riser (AMR)

A riser card is not a bus, but rather a card that attaches to the motherboard and allows inserting additional cards (called daughter cards). AMR slots typically provide sound or modem functions.

Communications Network Riser (CNR)

CNR is a riser card slot (not a bus) that allows for inserting networking, wireless communication, sound, or modem functions.