What is an Expansion Card?

Anurag Ghosh

An expansion card is an electronic circuit board that adds more functionality to a desktop computer. These cards are installed into the expansion slot of a computer motherboard, and they 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 enhance the three dimensional graphics processing power of a computer while a new sound card may improve a computer’s audio input.

A expansion sound card may improve a computer's audio input.
A expansion sound card may improve a computer's audio input.

There are alternative terms used for this type of card, and it is also known as expansion board, add-on card, interface adapter or an internal card. Generally, between one and seven expansion cards can be installed into the desktop computer system. Laptops do not use standard cards due to their small form factor, although they can often accept a removable PCMCIA card that offers additional functions.

Expansion cards such as a graphic card can add functionality when plugged into the motherboard.
Expansion cards such as a graphic card can add functionality when plugged into the motherboard.

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 resulted in modern forms of interface adapters that provided additional benefits beyond enhanced graphics and sound.

Most cards are inserted in PCI or “Peripheral Component Interconnect” slots, which are integrated circuits fitted onto the motherboard. One edge of the card holding the contacts or keys is inserted into the slot. This establishes an electrical contact between the motherboard and the card’s integrated circuits.

Standard interface adapters, such as graphics cards and sound cards, offer various added 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 may add functions for composing music, editing audio presentations, and other multimedia applications.

There are some “low-profile” cards that fit in a lower height computer framework. Some are used solely for external connectivity such as modem cards, storage area network (SAN), and network cards, which are commonly referred to as 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 can only be inserted on computers with available expansion slots. Computers such as the Apple Macintosh® and other all-in-one systems do not accept these cards.

Older computers require expansion cards to be plugged in using a USB rather than into the motherboard.
Older computers require expansion cards to be plugged in using a USB rather than into the motherboard.

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Discussion Comments


I had no idea that expansion cards had so many uses as I have essentially one main use for my expansion card slots. I, like @sammyG, am a video editor for a high-end video production company and require the use of both very expensive and highly specialized video expansion cards.

Many PC gamers will spend a few hundred dollars on the latest and greatest video card expansion and some will even add custom cooling and multiple cards to bridge and increase performance. My needs as a professional unfortunately require me to purchase the extremely-high end video workstation expansion cards.

These cards typically range in price from $1000 to $4000 and can often cost more then the computer system itself. The advantage that they add when processing and rendering special effects is well worth the money spent however.

The technology is constantly changing but the ability add onto my system and modify it through expansion cards makes the expense well worth it as my video editing is dependent on the reliable speed and excellent results that they provide.


@sammyG, thanks for the advice on storage. I am a Disc Jokey and own my own entertainment company where I offer services that include hours and hours of music choices. I think I will look into the storage options that are available.

My use of expansion cards has been mostly in the area of sound. There are many options available on the consumer market that will expand the options for digital music interfaces.

A lot of computers have excellent built-in audio systems and controller cards but there is a big difference between these consumer grade interfaces and the professional needs I have as a full-time disc jokey.

The ability to output into a purely digital and high-bit rate format is essential to providing my clients with the high-cost entertainment services that I charge for.

The computer can go beyond just jukebox functions however, and the ability for it to perform complex audio jobs is almost limitless. Between sound effects, beat matching and visualization control systems, my computer has it's hands full with tasks that require a professional grade sound expansion card.

Some of these cards on the market for audio pros include external interface components that make it easy for recording professionals and artists to connect important sound mixers, microphones and other audio devices.

Expansion cards are essential in my pursuit as a professional grade disc jokey.


The biggest use of specialized expansion cards that I have is for my external storage needs. If you have analyzed the local market for expansion cards you would find that one of the highest uses they have is for Redundant Array of Independent Disk systems held internally and externally from the controlling computer.

RAID expansion cards offer the ability for video editors like myself to get the speed and security that only several hard disks combined can offer. This is a sure bet for anyone with sensitive or data intensive computer needs.

Busy photographers can also benefit greatly from the use of expansion cards as the size files from modern digital cameras increase. As a side business I also photograph for a few select clients and as part of this I feel obligated to keep a reserve of these images so that clients in the future can contact me for additional prints.

The problem with this is that many of my desktop machines that I use to edit my photos simply do not have the space available on the internal hard drives to handle more then six months worth of portrait sessions.

This is where expansion cards come into play. Simply add another hard drive controller expansion card to one of the mother board's expansion slots and you can then add hard drives either externally or internally.


As a young computer nerd in my pre-teenage days I had several desires for expansion cards but they were mostly the older-style pcmcia laptop expansion cards. The ability for the archaic, hand-me-down PC notebooks that I managed to get my hands on was Universal Serial Bus capability.

USB was the hot subject at the time and was just making it's way onto the market. PS/2 and standard serial ports still had the share of compatibility so the dominated the available options for input devices of the time.

I'll never forget the day that my mom offered to purchase my first USB PCMCIA expansion card. It was like connectivity heaven. The options that opened up from there were like a nerd feast of the holidays.

My first device that I connected to my USB expansion card was an external Iomega 100 mega byte Zip Drive. The ability to go from storing 1.44 MB per 3.5 inch floppy disk to 100 MB Zip disks was the difference between night and day.

Expansion cards mean the ability to expand the needs of my system and to this day are a great way of extending the usability period of a desktop machine.

While laptop expansion cards have somewhat phased out the market in desktop users is still very strong with video cards dominated the share of business.

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