PCIe (peripheral component interconnect express) is an interface standard for connecting high-speed components. Every desktop PC motherboard has a number of PCIe slots you can use to add GPUs (aka video cards aka graphics cards), RAID cards, Wi-Fi cards or SSD (solid-state drive) add-on cards. The types of PCIe slots available in your PC will depend on your motherboard.
PCIe slots come in different physical configurations: x1, x4, x8, x16, x32. The number after the x tells you how many lanes (how data travels to and from the PCIe card) that PCIe slot has. A PCIe x1 slot has one lane and can move data at one bit per cycle. A PCIe x2 slot has two lanes and can move data at two bits per cycle (and so on).
You can insert a PCIe x1 card into a PCIe x16 slot, but that card will receive less bandwidth. Similarly, you can insert a PCIe x8 card into a PCIe x4 slot, but it’ll only work with half the bandwidth compared to if it was in a PCIe x8 slot. Most GPUs require a PCIe x16 slot to operate at their full potential.
PCIe cards also come in different generations: PCIe 1.0, PCIe 2.0 and PCIe 3.0 (PCIe 4.0 is not yet available but is on its way). Bandwidth doubles with each generation. How do you know what performance you’ll get with a PCIe expansion card? Your PCIe card will run at the lowest generation present. So if you put a PCIe 2.0 card in a PCIe 3.0 slot, you’ll get PCIe 2.0 performance.
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