Expansion Slot

What is an Expansion Slot?

An expansion slot in a computer is also known as expansion port or a bus slot alternatively. Ideally, it is a port or a connection inside the computer which is typically located on the motherboard or the riser card.

Over the years, all these different types of expansion ports have improved in design and functionality to a remarkable extent and through them you can now use different types of input and output devices. In short, these slots will help you to make a complete computer system.

Understanding Expansion Slot in Computer

Understanding Expansion Slot in Computer

Typically, an expansion port is a slot on the motherboard of a computer that allows inserting an expansion card that will enhance the functionality and performance of the system on the whole.

These expansion cards can be anything such as:

Ideally, if you want to make your computer to be useful and more productive allowing you to do the specific type of computing tasks that you want to do on it, you will need to make sure of one very important aspect.

That is, the CPU or the Central Processing Unit should be able to communicate with the outside world most efficiently.

This includes the other components of the motherboard as well as the different adapters or hardware devices that may be plugged into it externally.

This can only be facilitated by the expansion slots that allow connecting the adapters to the motherboard of the computer. These expansion slots have specific rules that allow them perform several important tasks such as:

When you add supplementary components to your main computer through these expansion ports, you actually add new features to your system which enhances the performance and capabilities of the system on the whole.

And, for that you do not need to mess with the innards of the computer or remove the computer casing even.

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These expansion slots simply give you a ‘plug and play’ option.

These expansion slots prove to be an extremely important and useful inclusion in the design of the motherboards which allows making easier, faster, and productive upgrades or customizing the system without much of a hassle.

This will allow you to do those specific tasks that you would not be able to do by using the main computer simply.

The design of the motherboards have also changed a lot over the years and the modern motherboards offer a lot of varied options to connect different types of external peripherals to the main computer.

The primary purpose of the expansion slots is to allow connecting hardware expansion cards to them depending on their types.

This means that these installation points should be compatible with the hardware device that you want to add to your computer.

The expansion cards inserted into the bus slots come with an edge connector. This allows it to snugly fit into the slot of the bus.

Apart from that, there is also a row of contacts designed in these expansion cards.

It is these particular contacts that establish an electrical connection between the electronics associated with the expansion card and the motherboard which mostly have Integrated Circuits or ICs.

Typically, there are different types of computer expansion slots available in the market. These are especially any one of the form as under:

There are also a few other types of bus slots that were used in the older computer motherboard models and a few are still used today in a few specific computer models. These are:

When you want to use an expansion slot to upgrade your computer system, it is elementary that you know about these differences in designs of the expansion slots along with their functionalities.

This is important because once you are able to distinguish among the expansion slots and the adapters you will be able to judge their respective compatibility.

Unless the two are compatible with one another the added hardware devices will not function the way you expect it to.

It is also important to know the limitations and abilities of each of these types of expansion slots while replacing computer parts or installing upgrades.

You can also use a riser card as an alternative to plugging in an adapter into the motherboard of the computer directly.

However, the purpose will be the same, albeit in a far-fetched way.

Typically, the riser board itself is plugged into the motherboard of the computer.

It can be inserted into the main board or can be attached to it with the help of screws.

The riser board will allow the users to use its own expansion slots to attach the adapter or hardware devices externally and thereby to the main board, indirectly.

Typically, the riser boards are used with desktop computer models of low profile and the rack-mounted servers.

A standard computer system will generally come with a number of expansion slots ranging anywhere between one and seven, depending on the design of the motherboard as well as the form factor of the case of the computer.

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However, in a backplane system, there can be as many as 19 expansion cards installed.

Uses and Working Process

Now, knowing a bit about the functions of the expansion slots in a computer, you may want to know more about its uses as well as the working process. Well, this article has that covered as well.

You can use the expansion slots to insert expansion cards that will allow you to add different devices and also provide a diverse range of functions including and not limited to:

In addition to that, if you insert a specific type of expansion card into the expansion slot it will also allow host adaptation such as Small Computer System Interface or SCSI and Redundant Array of Independent Disks or RAID interface.

If you intend to use some of the older expansion cards, it can also be used as:

Typically, the microcomputer in which a slot-type expansion card was supposed to be inserted as a card bus for the first time was Altair 8800.

This was designed and developed by the MITS or Micro Instrumentation and Telemetry Systems in 1974 and was designed based on the Intel 8080 processor.

Now, take a look at the working process of the expansion slots or bus slots.

These slots or openings are usually located at the back of the computer case.

It helps in establishing an electrical connection for the expansion card with the power supplied by the motherboard.

Usually, the expansion cards are attached to the slots with screws which ensure a snug fit and add to the security aspect as well.

As said earlier, the expansion ports allow inserting expansion cards such as video card, modem, network card, sound card and others so that the users can connect different hardware devices externally to their computers that are compatible with the expansion cards.

Actually, data is transferred to and from the expansion cards to the expansion slots and vice versa.

The expansion slots use the data lanes that they come with for this purpose.

These data pairs are basically signaling pairs that are used to send and receive data. Each of these data pairs typically comes with a couple of wires.

This creates a pathway to transfer data that has four wires in total. The data lanes can send data in packets of 8 bits in each direction at a time.

At this point, it is important to know that the PCI Express expansion ports usually come with different numbers of lanes to transfer data through. Typically, these ports can have 1, 2, 4, 8, 12, 16, or 32 lanes.

The number of lanes in a PCI Express port is indicated with an ‘x’ written as a prefix before the number of data transfer lanes present in it.

For example, if it indicates ‘x16’, it indicates that there are as many as 16 lanes in the slot.

Typically, the number of lanes is directly proportional to the speed of the expansion slot.

This means that higher the number of lanes, the faster will be the data transferred through the slot.

It is for this reason the video cards typically support an x16 lane port.

Questions & Answers:

What are the Common Types of Expansion Slots Found in a Computer and Devices Compatible to Those Slots?

The AGP port is used for inserting a video card, the AMR port for modem and sound card, the CNR port for modem, sound card, and network card, the EISA port for video card, SCSI, and network card, the ISA slot for sound card, video card and network card, the PCI slots for sound card, video card,

SCSI, and network card, the PCI Express slot for sound card, video card, network card, and modem, and the VESA bus slot is used for inserting a video card.

Are All Types of Expansion Slots Used Even Today?

No, of course. With the advancement in technology, most of the expansion slots mentioned above are obsolete now. As of now you will probably find the AGP, PCI, and PCI Express variants in the modern computers.

How to Determine the Number of Expansion Slots in a Computer?

Well, every motherboard design is different and therefore if you want to find out the number of expansion slots your computer has, you will first need to find out the manufacturer and the model of the motherboard. You can then find the exact specifications in the manual or on the internet.

Is it Feasible or Necessary to Use a Riser Board Today to Add Additional Hardware Devices Externally to a Computer?

Well, not really. Typically, it may be necessary in the case of older computers that typically have fewer expansion slots in them to add additional hardware devices to them externally.

But, the modern devices come with better and more advanced motherboards that are usually equipped with lots of options making it unnecessary to use a riser board any longer.

What is the Most Significant Advantage of Having Expansion Slots in Computers?

Though there are several advantages of having expansion slots in the computers, the most significant one is that these slots will allow you to replace an old video card with a new one without having to replace the entire motherboard with a new one. Therefore, it curbs down cost and hassles.

Do the Laptops Come with an Expansion Slot?

Usually laptops do not come with as many expansion slots as a desktop computer. Still, a few modern laptops come with PC Cards or PCMCIA or Personal Computer Memory Card International Association cards that can be inserted on their sides.

These are usually a memory of an I/O device of the size of a credit card. Some of the modern laptops may also come with a Cardbus slot which allows inserting an ExpressCard to the devices.


So, now you have a fair bit of knowledge about expansion slots after reading this article.

With this knowledge, you will not find it difficult to choose the best expansion slot to add the desired hardware device or adapter to your computer to enhance its functionality.