How Are PCIe Slots Numbered?

When it comes to building a desktop computer, one of the most important components is the motherboard. And when you look at a motherboard, one of the things that can be confusing is how PCIe slots are numbered. In this article, we’ll take a deep dive into how PCIe slots are numbered and what it means for your build.

First off, let’s define what PCIe slots are. PCIe stands for Peripheral Component Interconnect Express, and it’s a type of expansion slot used to connect devices like graphics cards, sound cards, and network adapters to your motherboard. These slots provide faster data transfer speeds than older expansion slot types like PCI or AGP.

Now, let’s talk about how these slots are numbered. The numbering system used for PCIe slots is based on the number of lanes each slot has. Lanes are essentially data transfer channels within the slot, and they determine how much data can be transferred at once.

The most common types of PCIe slots are x1, x4, x8, and x16. The “x” stands for the number of lanes in the slot. So an x1 slot has one lane, an x4 slot has four lanes, an x8 slot has eight lanes, and an x16 slot has sixteen lanes.

When numbering PCIe slots on a motherboard, the convention is to start with the topmost PCIe slot closest to the CPU socket as PCIe 1 or PCIEX1_1 (if it’s an ASUS motherboard), followed by PCIe 2 or PCIEX16_1 (if it’s an ASUS motherboard) below it if there are two or more identical slots on a single board.

The second group is usually labeled as 2 with 3rd being labeled as 3 and so on depending on how many groups there are.

It’s worth noting that not all motherboards have every type of PCIe slot available. Some budget motherboards may only have one or two PCIe slots, while high-end gaming motherboards may have multiple x16 slots for running multiple graphics cards in SLI or CrossFire.

In addition to the numbering convention, there are a few other things to keep in mind when it comes to PCIe slots. One is that PCIe slots are backwards compatible. So if you have a graphics card that requires an x16 slot, it will work in an x8 or x4 slot as well (although at reduced performance).

Another thing to consider is that some motherboards may share lanes between PCIe slots. For example, if you have two x16 slots on your motherboard and you install a graphics card in both of them, they may both run at x8 speeds instead of x16 because they’re sharing the same lanes.

In conclusion, understanding how PCIe slots are numbered is important when building your own computer or upgrading an existing one. By knowing which slot is which and how many lanes each slot has, you can make informed decisions about which components to install and where to install them for optimal performance.