Describe the purpose of an adapter card and the role of an expansion slot.

Adapter cards increase the functionality of a computer by adding controllers for specific devices or by replacing malfunctioning ports. Figure 1 shows several types of adapter cards, many of which can be integrated into the motherboard. These are some common adapter cards that are used to expand and customize the capability of a computer:

  • Network Interface Card (NIC) - Connects a computer to a network using a network cable.

  • Wireless NIC - Connects a computer to a network using radio frequencies.

  • Sound adapter - Provides audio capability.

  • Video adapter - Provides graphic capability.

  • Capture card - Sends a video signal to a computer so that the signal can be recorded to the computer hard drive with Video Capture software.

  • TV tuner card - Provides the ability to watch and record television signals on a PC by connecting a cable television, satellite, or antenna to the installed tuner card.

  • Modem adapter - Connects a computer to the Internet using a phone line.

  • Small Computer System Interface (SCSI) adapter - Connects SCSI devices, such as hard drives or tape drives, to a computer.

  • Redundant Array of Independent Disks (RAID) adapter - Connects multiple hard drives to a computer to provide redundancy and to improve performance.

  • Universal Serial Bus (USB) port - Connects a computer to peripheral devices.

  • Parallel port - Connects a computer to peripheral devices.

  • Serial port - Connects a computer to peripheral devices.

Computers have expansion slots on the motherboard to install adapter cards. The type of adapter card connector must match the expansion slot. The different types of expansion slots are shown in Figure 2.

A riser card was used in computer systems with the LPX form factor to allow adapter cards to be installed horizontally. The riser card was mainly used in slim-line desktop computers.

Communications and Networking Riser (CNR) is a special slot used for some networking or audio expansion cards. The CNR is not in use any more because many of the functions of the CNR are now found on-board the motherboard.

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An adapter card (also known as an expansion card) is simply a circuit board you install into a computer to increase the capabilities of that computer. Adapter cards come in varying formats for different uses, but the important thing to note is that no matter what function a card has, the card being installed must match the bus type of the motherboard you are installing it into. For example, you can only install a PCI network card into a PCI expansion slot.

For today's integrated components, you might not need an adapter to achieve the related services, but you will still need to install drivers to make the integrated devices function with the operating system. As this trend was maturing, ...

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Describe the purpose of an adapter card and the role of an expansion slot.

An expansion slot refers to any of the slots on a motherboard that can hold an expansion card to expand the computer's functionality, like a video card, network card, or sound card.

The expansion card is plugged directly into the expansion port so that the motherboard has direct access to the hardware. However, since all computers have a limited number of expansion slots, it's important to open your computer and check what's available before you buy one.

Some older systems require the use of a riser board to add additional expansion cards; however, modern computers not only usually have enough expansion slot options, but they also have features integrated directly into the motherboard, eliminating the need for so many expansion cards.

ASUS 970 Pro Gaming/Aura ATX DDR3 AM3 Motherboard.

Expansion slots are sometimes referred to as bus slots or expansion ports. The openings on the rear of a computer case also sometimes go by this term.

There have been several types of expansion slots over the years, including PCI, AGP, AMR, CNR, ISA, EISA, and VESA, but the most popular one used today is PCIe. While some newer computers still have PCI and AGP slots, PCIe has basically replaced all the older technologies.

ePCIe (External PCI Express) is another kind of expansion method, but it's an external version of PCIe. That is, it requires a specific kind of cable that extends from the motherboard out the back of the computer, where it connects with the ePCIe device.

Like mentioned above, these expansion ports are used to add various hardware components to the computer, like a new video card, network card, modem, sound card, etc.

Expansion slots have what's called data lanes, which are signaling pairs that are used for sending and receiving data. Each pair has two wires, which makes a lane have a total of four wires. The lane can transfer packets eight bits at a time in either direction.

Since a PCIe expansion port can have 1, 2, 4, 8, 12, 16, or 32 lanes, they're written with an "x," like "x16" to indicate that the slot has 16 lanes. The number of lanes directly relates to the speed of the expansion slot, which is why video cards are usually built to use a x16 port.

An expansion card can be plugged into a slot with a higher number, but not with a lower number. For example, a x1 expansion card will fit with any slot (it will still run at its own speed, though, not the speed of the slot) but a x16 device will not physically fit into a x1, x2, x4, or x8 slot.

When you're installing an expansion card, before removing the computer case, be sure to first power down the computer and unplug the power cord from the back of the power supply. The expansion ports are usually located catty-corner to the RAM slots, but that might not always be the case.

If the expansion slot hasn't been used before, there will be a metal bracket covering the corresponding slot on the back of the computer. This needs to be removed, usually by unscrewing the bracket, so that the expansion card can be accessed. For example, if you're installing a video card, the opening provides a way to connect the monitor to the card with a video cable (like HDMI, VGA, or DVI).

When seating the expansion card, make sure you're holding on to the metal plate edge and not the gold connectors. When the gold connectors are properly lined up with the expansion slot, press down firmly into the slot, making sure that the edge where the cable connections are is easily accessible from the back of the computer case.

You can remove an existing expansion card by holding on to the metal plate edge, and pulling firmly away from the motherboard, in a straight, upright position. However, some cards have a small clip that keeps it in place, in which case you have to hold back the clip before pulling it out.

Whether or not you have any open expansion slots varies with everyone since not all computers have the exact same hardware installed. However, short of opening your computer and checking manually, there are computer programs that can identify which slots are available and which are used.

For example, Speccy is one free system information tool that can do just that. Look under the Motherboard section and you'll find a list of the expansion slots found on the motherboard. Read the Slot Usage line to see if the slot is used or available.

Another method is to check with the motherboard manufacturer. If you know the model of your specific motherboard, you can find out how many expansion cards can be installed by checking with the manufacturer directly or looking through a user manual (which is usually available as a free document from the manufacturer's website).

If we use the example motherboard from the image at the top of this page, we can access the motherboard's specifications page on the Asus website to see that it has two PCIe 2.0 x16, two PCIe 2.0 x1, and two PCI expansion slots.

One more technique is to see which openings are unused on the back of your computer. If there are two brackets still in place, there are most likely two open expansion slots. This method, however, isn't as reliable as checking the motherboard itself, since your computer case might not correspond directly with your motherboard.

Laptops don't have expansion slots like desktop computers do. A laptop may instead have a little slot on the side that uses either PC Card (PCMCIA) or, for newer systems, ExpressCard.

These ports can be used similarly to a desktop's expansion slot, like for sound cards, wireless NICs, TV tuner cards, USB slots, additional storage, etc.


  • What is gradually replacing portable-specific expansion slots?

    USB (Universal Serial Bus) is a standard connection for various devices. Many manufacturers now use USB instead of portable-specific expansion slots.

  • What screws do you use on PCI expansion slots?

    Most computer case screws require #6-32 x 1/4-inch screws. They typically have a hexagonal head and can be installed or removed using a #2 size Phillips screwdriver.