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.


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.