Motherboard Expansion Slots – CompTIA A+ 220-1101 – 3.4

If you want to add features to your computing platform, it’s common to use the built-in expansion slots. In this video, you’ll learn how to use expansion slots to upgrade and enhance your personal computer.

If you look at a motherboard, there are a lot of different components that are attached to these systems. There’s CPU and memory and storage and expansion slots, and there needs to be some way that all of these different components can communicate with each other. There are also times when we might want to add additional functionality to our motherboard by adding an expansion card into one of the available slots. And that expansion card needs some way to communicate with the memory and the CPU.

Many of these components on the motherboard have some level of modularity, so there has to be some way that all of these can communicate with each other. To be able to communicate between the CPU and memory, for example, the computer has a series of communications paths called a bus. If you look at the bottom of your motherboard, you can see the buses much clearer. You could see the traces are moving between the different components on your motherboard. And you can see very clearly where the communication paths happen to be.

If you’re working with an older computer, you may see some expansion slots on that computer that are PCI. This is Peripheral Component Interconnect, and it’s a standard that’s been around since 1994. PCI has different bus sizes that could be used. There’s a 32-bit PCI bus and a 64-bit PCI bus. And these communicate using parallel communication.

This is a type of connector that you might find on legacy devices. You’re probably not going to find a lot of PCI interfaces on your newest computers. Here’s an example of this parallel bus. You can see I have two different 32-bit PCI expansion slots, and they are all sharing that same communications path back to a central controller on the motherboard.

The 64-bit expansion slot is effectively the same thing. We still have parallel communication and sending all 64 bits across the bus at the same time. But obviously, the 64-bit bus is twice as large as the 32-bit bus. Physically, the 64-bit interfaces are also much larger than the 32-bit. You can see the 64-bit PCI slots there at the top and the 32-bit PCI slots at the bottom.

Our PCI expansion cards not only support different widths, but they also support different voltages. This particular 32-bit PCI card has a slot in the card itself that designates a 3.3-volt capability or a 5-volt capability. Here’s the larger 64-bit PCI expansion card. Everything that’s on the back of this card has extra contacts that designate the 64-bit width of this bus. And this card has keys that also designate that it supports 3.3 volts and 5 volts of power.

Here’s another look at these interfaces on the motherboard. You can see, those keys are in very specific spots so that it will only allow the correct card to be installed onto the motherboard. Let’s look at this 64-bit card that we had earlier. We know that this card was a 64-bit card because it had that 64-bit key and the additional contacts on the back of the card. We also know that this card supports 3.3 volts of power.

And you can see there is a key in the adapter that does show the 3.3 volt is being used. To install the card, we would put it right on the top of that PCI interface, and then we would gently press down so that all of these contacts are going directly into the slot itself on the motherboard. If it’s difficult to see those copper contacts, then we’ve installed this card properly. We can screw it down into our computer case using the connector at the top of the card.

On newer computers, you probably won’t find a PCI bus. Instead, you’ll find the newer PCI express bus. You’ll sometimes see this written as PCIe with the lowercase e. This effectively replaces PCI, and it changes the way we communicate across this bus. Instead of a parallel connection, PCI express uses a serial connection. And the communication path that it uses to communicate between these PCI express devices is called a PCI express lane.

Just as you add more lanes to a highway to support more traffic, you can add more lanes to a PCI express bus to support the transfer of more data. You’ll see these lanes referred to as a 1, 2, 4, 8, 16, or 32 full-duplex lane. These are written with an x at the beginning, so you’ll sometimes see x1, x2, x4, and so on. Normally, we would pronounce this with the x being a by. So this is a by 1, by 2, by 8, or by 32, for example.

This image really shows the simplicity of a serial connection between devices. This PCI express 1 by lane has one communications path going one direction and another going the other direction. Both of those together are the PCI express 1 by connection. If we need more bandwidth between these two devices, then we use an expansion slot that has more lanes. This is a PCI express by 4 lanes, and you can see, all four of those communication paths between the PCI express device A and PCI express device B.

Here’s a motherboard that supports both PCI and PCI express on the same motherboard. You can see the spot for the CPU and the memory, and all of the expansion slots are in the upper left. Let’s zoom in on those and really see what’s here. We have two PCI slots on the left side, and then we have PCI express slots on the right side. You can see some of these PCI express slots have a larger number of lanes than perhaps the by 1 lanes that are much smaller on the motherboard.

PCI express adapter cards look very similar to the PCI, but the slots and the number of contacts on the card are very different than a PCI adapter. Many PCI express cards also have this hook right here at the end that helps lock the card into the slot itself. To install a PCI express adapter, you would usually put that hook or lock into the adapter slot first and then push down very gently to slide the rest of the card down into the adapter slot.

You want to make sure that you have everything lined up properly with the card and that you’re not pushing too hard. If the card is not installing, then you should pull it back out, have a look at the different settings on your card and on the slot, and then try installing the card again. If you have everything aligned, then this card should slide into the slot very easily, and you can lock it in place with the screw connection on the case.