The Purpose of Expansion Slots


An expansion slot is a part of your computer's motherboard where you can attach additional circuit boards to boost functionality and performance of your PC. Expansion slots are generally only found on tower PCs, not on laptops or netbooks because of size issues. These slots will be accessible by opening your tower and also removing a small metal or plastic plate located on the back of your tower so any external components of your expansion, such as ports, will be accessible.

Expansion Slots

  • Upon opening your PC tower and locating your motherboard, you will probably see a few long, thin slots that allow you to plug in expansion cards. These slots are how your computer reads things like graphics cards, sound cards and network cards. You can also use an open slot to add a memory expansion to your computer which could improve performance. These cards easily fit into their designated holes and are secured in place by either a screw or clamps where the expansion card's physical interface protrudes from the back of your system tower.


  • There are many different standards associated with expansion slots. Though too numerous to name them all, the most common standards are PCI, PCI Express, and AGP. One of the most important factors to keep in mind when purchasing new upgrades for expansion slots is which type of standard your slot conforms to. For example, you can't plug a card made for PCI Express slots into an AGP slot, it wouldn't fit, and if it did fit, it still wouldn't work.

PCI and PCI Express

  • PCI, short for peripheral component interconnect, is one of the most widely used expansion slots on motherboards. PCI is the predecessor to PCI Express, a smaller and faster version with the same basic functions. These slots are most commonly used to connect sound cards and network cards but have other uses, such as adding extra USB ports. As computer game graphics get more advanced, PCI is less capable of handling graphics cards as well, yet PCI Express can handle the more powerful video cards of today.

AGP slots

  • AGP, short for advanced graphics port, is a slot used specifically for graphics cards. These slots allow your card to directly access your computers system memory, which speeds up graphics processing. When it comes to performance, AGP slots are less advanced than PCI Express, which does the same things AGP does but faster. When you are using more than one graphics card it is common to have one AGP card and one PCI Express card, as computers generally don't have two AGP slots on the motherboard. Some motherboards have two PCI Express slots, however, so dual video card configurations using only PCI Express are now fairly common.


  • If you have no open expansion slots on your motherboard, or you have a laptop, fret not. Alternatives are available. Some of the things done through expansion slots are now commonly done through ExpressCard and USB slots. ExpressCards allow laptop owners to enjoy some of the functionality afforded to desktop owners through their expansion slots. These are basically externally accessed expansion slots that can be used for wireless cards and other peripherals.

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