What Is A Computer Expansion Card? (Explanation And Types)

Expansion cards have been around since the very early days of desktop computers. In this post, we will explain what an expansion card is and the different ways it can benefit you.

A computer expansion card is a PCB with components and an edge connector that plugs into a motherboard to expand a computer’s functionality.

The most commonly used type of expansion card slot used today is PCI Express and its variants which we will cover more in-depth in this article.

Expansion cards are typically something that can be installed into a new computer you’ve purchased or added as an upgrade part to increase the capabilities of a computer after the purchase.

Now that you know, in short, what an expansion card is, let’s look at the physical and practical aspects to allow a deeper understanding of what they are.

What an expansion card looks like (and its parts)

Here is an image of a typical expansion card.

The parts of an expansion card and what it looks like.

As you can see, the card has copper-plated contacts along with the edge connector, which fits into an expansion slot (or bus slot) on a motherboard.

We will cover the different types of slots later, but for now, I’m just pointing out that the contacts of the expansion card make contact with the motherboard’s slot contacts.

The motherboard slot is usually designed so that the contacts provide a small amount of spring tension against the contacts of the card.

Along the card’s front side, you can see the metal bracket (sometimes referred to as a backplate) that acts as the primary support and gets screwed to the computer case.

This plate usually contains connectors or, in the case of a graphics card, small vents to help with venting hot air.

These connectors provide the connectivity to interface external devices with the expansion card and, finally, the computer.

The function of a computer expansion card

A variety of expansion cards for a computer.

As I’ve already mentioned, an expansion card adds functionality to a computer by providing the necessary hardware to carry out tasks that the computer otherwise would be incapable of doing without it.

In some cases, though, it might be to perform something that the computer can already do.

Two main reasons may include:

  1. To replicate an existing ability for specific real-world requirements that require more than one instance of that ability.
  2. To provide the same overall function but with improved deliverability. The improvement may be quality, improved functionality, or other end-user benefits.

Now that you understand what the function of an expansion card is let’s go over the actual workings of a card.

How they work

Cards can be designed to work in two main ways. Let’s take a look at both designs to understand each one a little better.

1. To add functionality by using hardware on the card only

Some expansion cards don’t have connectors of any kind on the mounting plate or connect to any cables that provide connectivity somewhere outside of the computer.

Here are some examples of this:

  • M.2 Expansion cards: An expansion card with M.2 slots allows extra SSDs to be added.
  • RAM Drives (Like iRAM): An card that holds RAM modules that can be used as a drive that provides high-performance levels.
  • Internal IO expansion cards: Cards that provide expanded connectivity for internal IO when a motherboard lacks enough outputs, like an M.2 expansion slot for SSDs, to mention one example.

Drivers from the manufacturer are usually required for an expansion card to work at its best. Simply put, a driver is software that gets installed to allow the computer to communicate properly with it and to be able to use all the features correctly.

Computer software can give instructions to the expansion card hardware, with the driver acting as the final instruction delivery to tell the hardware what to do in a more specific manner.

This all happens between running instructions to and from memory and the CPU through the computer’s bus and to the expansion card.

2. To act as an intermediary

These cards allow for external components to be connected to it via mountable sockets or connectors on the fastener or mounting plate.

The same type of communication happens as mentioned with the previous type of card, except that there are external connectors that the card processes and relays to the computer’s bus.

Various types of computer expansion slot on a motherboard

There have been many generations of bus slots that have improved over time since the earliest version of desktop computers.

An abbreviated list of standard slots over time for desktop PCs goes as follows:

Expansion SlotDescription & Launch Year
An 8 Bit ISA slot.16-Bit
A 16 Bit ISA slot.
Industry Standard Architecture (ISA) 8 & 16-bit – 1981
An EISA slot.Extended Industry Standard Architecture (EISA) – 1988
A Vesa Local Bus slot.VESA Local Bus (VL-Bus) – 1992
A PCI slot.Peripheral Component Interconnect (PCI) – 1992
An AGP slot.Accelerated Graphics Port (AGP) (Graphics Cards Only) – 1997
A PCI-X slot.Peripheral Component Interconnect eXtended (PCI-X) – 1998
A PCI Express slot.Peripheral Component Interconnect Express (PCIe) – 2003
Types of expansion card slots over time for desktop PCs.

With AGP and PCI Express slots, different versions were produced, changing the layout of the AGP slot somewhat.

The different AGP slot versions and their layout.

Thanks to the original uploader JigPu at English Wikipedia. Later versions were uploaded by Aluvus at en.wikipedia., CC BY-SA 2.5, via Wikimedia Commons for the image.

However, with PCI Express slots, the slot doesn’t look any different, but the performance improves with each version.

PCI Express slots also come in four different sizes, delivering different performance levels.

PCI Express SlotsDescription
A PCI Express x1 slot.PCIe x1 (One data lane.)
A PCI Express x4 slot.PCIe x4 (Four data lanes.)
A PCI Express x8 slot.PCIe x8 (Eight data lanes.)
A PCI Express x16 slot.PCIe x16 (Sixteen data lanes.)
Various PCI Express slot sizes.

Laptops also have expansion slots called Personal Computer Memory Card International Association (PCMCIA).

But now that we have USB-C and Thunderbolt offering fast peripheral connectivity, expansion slots PCMCIA or ExpressCard are no longer required.

Examples of computer cards

Here are some examples of expansion cards that you may encounter:

  • Sound cards: Adds the ability for a computer to output audio or receive audio from external devices.
  • IO Expansion cards: They can add additional ports, connectors, or slots for various media storage, communication components, or devices.
  • Graphics cards: Graphics cards are undoubtedly the most commonly added expansion card for computers today. They offer the ability for improved graphics performance for games or other software that require accelerated 3D graphics. The hardware on the card is designed to compute graphics workloads in the most efficient and specific manner. Everything from the graphics processing unit to the GDDR memory is optimized for this task alone.
  • RGB Lighting cards: Cards that control ARGB lighting with software providing various lighting effects or profiles.
  • Codec cards: They are designed to specifically accelerate the encoding and decoding of video media using hardware instead of relying on software decoding utilizing the CPU.
  • Video capture cards: This card type is designed to take video and audio signals from external sources and stream them through software that can store the content in standard reusable file formats.
  • Network cards: Network cards (NIC cards) provide the ability to connect wireless or wired network connections to a computer. Often, they will be installed to allow a newer or faster type of network connectivity than the motherboard can, thus avoiding a complete motherboard replacement.
  • TV Tuner cards: These cards allow your computer to view broadcasted channels via satellite or antennas. Other benefits include recording live TV or having media software that can offer other standard television features like electronic guides or schedules.
  • DAC cards: Designed for audio professionals or hobbyists that need better connectivity to DAW software or other music or audio-related applications.

There are, of course, many more examples of computer expansion cards, but these are probably the more well-known list.

Where they came from

An old IBM computer.

The first implementation of an expansion slot was in the first commercially available microcomputer called a Micral N in 1973. And later, the first produced version as a standard slot in the Altair 8800 was named the S-100 bus.

From there, descendants were born and implemented by Apple (which included their proprietary versions) and IBM PC.

Further generations were developed, leading to the slots we know today.

Issues that can arise with them

Anything implemented as an end-user expansion or replacement in the electronics world can present certain potential risks for reliability issues.

1. Contacts

The first and most obvious is making contacts as reliable as possible.

Without electrical contacts offering as little resistance as required, these cards’ unreliable and sometimes improper functioning is inevitable.

In this case, it is best to clean the contacts of the cards using the eraser method.

However, a high level of care must be taken to avoid leftover rubber filings from the cleaning process from remaining behind on the cards before reinstalling them securely back into place.

This cleaning method avoids relying on solvents that can potentially damage sensitive electronics and provides a higher level of cleaning without compromising the copper material forming the contacts.

The same method is shown for cleaning RAM contacts in my other blog post in case you need to clean the contacts of a computer’s expansion card.

2. Fans and cooling

Another issue that can arise is cooling fans becoming worn out on expansion cards that have active cooling.

Most commonly, these types of cards will be graphics cards. However, fans eventually become worn and can cause a rattling sound or seize up where they no longer provide any cooling, causing an overheating situation and becoming a fire hazard.

3. Sagging

This is an issue that arises more commonly with graphics cards.

Because graphics cards require a substantial amount of cooling, the heatsinks for the cooling assembly turn out to be pretty heavy.

This weight over time and the added heating up and cooling down causes the card to sag.

The most significant cause of this is from manufacturers that don’t include a strong enough frame that should reinforce the card.

Ideally, a strong reinforcement along the top edge of the card that attaches to the case bracket would go a long way to avoiding this problem.

Some third-party manufacturers have a range of products to help avoid this issue.

Vertical and horizontal support braces or brackets are available, even with RGB lighting, to add some extra aesthetics.

Read more about graphics card sagging.

Mini expansion cards and the various types

A M.2 SSD used in both desktop, all-in-one, and laptop computers.

These expansion cards are not only used for desktop computers but for laptops too.

Here are some examples of mini-expansion cards:

  • mSATA: These expansion slots are used for SSDs on laptops and desktops.
  • mPCIe: Because this slot uses the PCI Express interface, it isn’t only confined to supporting SSD cards. Commonly found in laptops and desktop motherboards. In addition, this connector offers a way to plug in miniature expansion cards.
  • M.2: This is the newer technology of the three and offers excellent performance and power management. M.2 is an excellent option for laptop and desktop motherboards for various applications of expansion cards.

M.2 Devices come in various sizes and different keyed slots. So bear this in mind when purchasing any components for mini-expansions slots.

Make sure you have the correct part matched for the slot type. These slots can be easily mistaken as they bear a similar physical resemblance and require careful observation to identify them.

A CPU Card that plugs into a motherboard

A CPU expansion card is being installed into the motherboard's slot.

Certain models of computers included a CPU on an expansion card instead of a CPU and a socket directly on the motherboard.

While you probably won’t find many today, as they weren’t used in many generations of CPUs before they were phased out.

They were also used to augment the processing capabilities of computers by increasing the number of CPUs and, in some cases, expanding the memory.

CPU cards were produced for various chassis including PCI, PC/104, ISA, PXI, and ETX.

Is a graphics card considered an expansion card?

A graphics card is most certainly an expansion card, yes. It bears all the attributes of an expansion card and typically comes in some or other version of a PCI Express slot.

Graphics cards are fitted or installed the same way any other expansion card is and, more often than not, take up two standard slots from your computer case.

Like many other cards, graphics cards offer connectivity on the mounting plate to monitors or screens that display the processed information from the graphics card.

What is a daughterboard?

A daughterboard, riser slot, or mezzanine board.

A daughterboard is a type of expansion card that offers connectivity directly to a motherboard as opposed to the computer bus.

Occasionally daughterboards are designed as riser slots that allow an expansion card to be plugged in to lay parallel to the motherboard.

It is sometimes referred to as mezzanine cards because it resembles the stacking layout of mezzanine theaters.

Daughterboards are used in a wide array of different computer hardware technologies like Arduino boards, Robotics, and CPU socket daughterboards to mention a few examples.


And that covers most of what you need to know about an expansion card.

There are so many variants and applications for expansion cards that it could take a long time to research them all.

However, if you need to add unique functionality to your computer that isn’t available ordinarily, rest assured there is a high likelihood that some company has designed something you can implement.

In rare cases, you may find solutions that you couldn’t have imagined is out there.

Either way, expansion cards have been a lifesaver on several occasions when needing more customized computing solutions for specific company requirements that I’ve consulted with.

So if you find something lacking from your computer, don’t hesitate to do some research to see if something is available.