Expansion cards add functionality to desktop computers by being installed in the motherboard’s expansion slot. Video and sound cards are common examples. Laptops use PCMCIA cards. The Altair 8800 was the first microcomputer to add an expansion card bus. Most cards are plugged into PCI slots. Standard interface adapters offer various functions, while low profile cards fit into smaller computer frames. Some cards are used for external connectivity, and a PC expansion card only fits into computers with available expansion slots.
An expansion card is an electronic circuit that adds more functionality to a desktop computer. These cards are installed in the expansion slot on a computer’s motherboard and allow the computer to perform additional functions not offered by the motherboard. Video cards and sound cards are common examples: a new video card added will improve a computer’s three-dimensional graphics processing power while a new sound card might improve a computer’s audio input.
There are alternative terms used for this type of card and it is also known as an expansion card, add-in card, interface adapter, or internal card. Typically, one to seven expansion cards can be installed in your desktop computer system. Laptops do not use standard cards due to their small form factor, although they can often accept a removable PCMCIA card which offers additional functions.
The Altair 8800, developed in the mid-1970s, was the first microcomputer to add an expansion card bus. In 1981, IBM® launched its first PC with an XT bus, which was later replaced with a 16-bit ISA. The introduction of the PCI bus in 1991 led to modern forms of interface adapters that provided additional benefits beyond improved graphics and audio.
Most cards are plugged into PCI or “Peripheral Component Interconnect” slots, which are integrated circuits mounted on the motherboard. An edge of the card that contains the contacts or keys is inserted into the slot. This establishes electrical contact between the motherboard and the card’s integrated circuits.
Standard interface adapters, such as graphics cards and sound cards, offer various additional functions. Some video cards offer video capture, MPEG 2 and MPEG 4 decoding, a light pen and the ability to connect to multiple monitors, for example. Sound cards can add features for composing music, editing audio presentations, and other multimedia applications.
There are some “low profile” cards that fit into a lower height computer frame. Some are used exclusively for external connectivity such as modem cards, storage area network (SAN), and network cards, commonly called I/O cards or input/output cards. A USB card is mainly used by users who need additional USB or Firewire ports.
A PC expansion card fits only into computers with available expansion slots. Computers such as the Apple Macintosh® and other all-in-one systems do not accept these cards.
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