Why Do Motherboards Have Multiple PCIe Slots?

A motherboard is the central printed circuit board (PCB) in computers and other expandable systems. It holds and allows communication between many of the crucial electronic components of a system, such as the central processing unit (CPU) and memory, and provides connectors for other peripherals. But why do motherboards have multiple PCIe slots?

The answer lies in the nature of the PCIe bus. PCIe is a point-to-point serial protocol, meaning that each device connected to the bus has its own dedicated connection to the PCIe controller on the motherboard.

This contrasts with earlier buses like PCI, which were shared buses with multiple devices sharing a single connection.

The benefits of using a point-to-point bus are numerous. For one, it allows for much higher data rates than a shared bus.

Furthermore, it eliminates potential bottlenecks caused by one device hogging the bus and slowing down communication for everyone else.

Another key benefit of PCIe is that it allows for devices to be connected in different topologies. The most common topology is called “x16,” where 16 lanes of data are used for communication between the device and the motherboard.

However, there are also x1, x4, and x8 topologies. The number of lanes corresponds to the width of the connection between the device and the motherboard—a wider connection can carry more data.

So, why would you want to use a different topology than x16? The answer is simple: flexibility and cost. Not every device needs 16 lanes of data—for example, a simple network card may only need one lane.

And using a smaller topology means that fewer pins are required on both the device and the motherboard, which can save money.

The flexibility afforded by PCIe is one of the key reasons why motherboards have multiple PCIe slots. By having multiple slots, motherboard manufacturers can offer support for a wide variety of devices without having to make trade-offs in terms of cost or performance.

One final note: while PCIe is today’s standard bus protocol for connecting devices to motherboards, it’s not the only option out there. Another popular choice is Thunderbolt 3, which uses a different type of connector but shares many of the same advantages as PCIe.