If you were to look at a motherboard, it almost seems like a small city that's seen from the air. There are a lot of different areas of the motherboard and it seems like there is some type of connectivity between all of these different components. That connectivity is what we refer to as a computer bus. This bus is a pathway that connects the different components of your motherboard to each other. For example, there's a bus between your memory slots and your CPU. There's also a bus that connects all of your expansion slots. These different buses allow us to connect all of these very diverse components on the motherboard to each other so that they work as one single unit. These buses also allow us to increase the functionality of our motherboard. For example, the buses that connect all of the different expansion slots together allow us to put additional cards onto our motherboard, thereby increasing the functionality of that system. If you were to look closely at your motherboard, you can see the individual buses or pathways that are used to move information from one part of the motherboard to another. And if you're curious, you could trace one end of a bus connection all the way around the motherboard to where it connects on the other side. On older motherboards, you may find that one of the buses available is a PCI bus. This stands for peripheral component interconnect. This is one that was created in 1994 and has two different sizes, a 32-bit bus and a 64-bit PCI bus. This older style bus sends data over a parallel communication. You may find that your newer motherboard no longer has a PCI bus and instead uses PCI Express, which has a serial form of communication. We mentioned that there are two sizes to the PCI bus. There's the 32-bit and the 64-bit. The 32-bit PCI bus is shown here. And you can see there are 32 separate connections between the different devices. This means when you want to send 32 bits, that one bit at a time is sent across this 32-bit bus all simultaneously. And hopefully all 32 of those bits will appear at the same time on the other side. A 64-bit bus is exactly the same form of communication, but instead of sending 32 bits across 32 separate lines, you send 64 bits over 64 separate lines in this PCI bus. This is an example of a 32bit PCI bus and a 64-bit PCI bus. This is where you would plug in your expansion cards. And if you look closely at the motherboard, you can see all of these small traces that are connecting these different bus connections together. You'll notice on these slots that there are small tabs or keys that are in the middle of this connector. Those are to designate different power settings for the adapter cards that you're plugging in. For example, your expansion cards will have these small slots that are in the connector, and that's what's sliding into those adapter card slots on the motherboard. A 64-bit expansion card has additional connectors on the bottom and it has a separate keyway that designates that this is a 64-bit expansion card. Installing an adapter card onto a motherboard simply requires that you push the card directly into that slot. So, if you have a PCI slot, you would simply put the adapter card right on top of the slot so that all of those individual keyways are properly aligned. And then you would push the card down very carefully onto the motherboard, being very careful not to give too much pressure or you might end up breaking components on that motherboard. Once it's pushed in, you can see that it fits relatively snugly. This one should probably be pushed in just a little bit further so that you can no longer see any of those copper connections. But once it's in place, it's commonly screwed down onto the computer case so that it can't accidentally be removed from that slot. PCI Express or PCIe is a newer type of bus and this is probably the bus type you'll find on the most recent computers. PCI Express communicates over a serial connection. This is very different than the parallel pathways we saw with PCI because with PCI Express and a serial connection, we're simply sending one bit at a time over the same pathway. You'll often hear us refer to these PCI Express pathways as lanes of communication. So if you're looking at a motherboard and there is an interface labeled PCIe X1, it's referring to the number of lanes available for that particular interface. The X1 is pronounced BY1. X2 would be by 2, by 4, by 8, and so on. So when we're looking at that PCIe ex1, this is really a PCI Express interface with a BY1 connection. Since the pathways that we use to communicate for PCI Express are serial, we don't have to have those wide 32bit or 64-bit pathways. We can simply have one pathway going one direction and one pathway going the other direction. This would be referred to as a PCI Express by one lane where you have a single lane going one way and a single lane going the other. That means if you wanted a PCI Express by four lanes, you would have four of those and you would effectively be quadrupling the amount of throughput that you could have compared to a PCI by one. Here's a motherboard that has both PCI interfaces and PCI Express on the same motherboard. You'll notice that they look very similar to each other. But if you look closer, you'll notice that the keyway for PCI is further back away from the edge of the motherboard. And for PCI Express, that keyway is closer to the edge of the motherboard. You'll also notice that the size of the slots may be different depending on the bus type. For example, this is the shortest PCI interface. This is a 32-bit interface. And this is the shortest PCI Express interface which is the by one interface. This means if we only need the throughput provided by a PCI BY1 interface, we can use that smaller connection and save that room on our motherboard. The PCI Express interface cards look very similar to the PCI interface cards, but if you look closer, you'll notice you have that keyway that's closer to the edge of the motherboard. Many of these PCI Express adapter cards also have a small hook on the back of the interface cards that fit into a connector that's on the motherboard. This fastens the card down not only at the keyway that's connected to the chassis of the computer case, but it also connects it to the motherboard itself. When you're removing a PCI Express card from the motherboard, you want to be sure that you're not only removing the screw that's connecting it to the case of the computer, but you also unlatch that connector that's holding it in on the other side.