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What is a PCIe Expansion Slot? 
PCI Express (PCIe) is a standard interface that connects peripheral components or add-on cards to the motherboard. PCIe can also be described as a standard for connecting devices to computers. The internal structural design of PCIe is a lot like a local area network in that each link goes a central hub in the computer that performs network-like switching. When the PCIe card is installed, a connection or link is formed between the PCIe device and the system. The link is constructed around a bi-directional serial point-to-point connection called a “lane”. A link can use more than one lane at a time by all links compliant with the PCIe specification, but must minimally support single-lane connections, known as “x1” links. For greater potential bandwidth, PCIe devices and systems have the option to support links using multiple simultaneous lanes. The size of a PCIe card is determined by the number of lanes. There are four sizes: x1, x4, x8, and x16. The number "x" refers to how many lanes there are in a PCIe slot. For example, a PCIe x 16 means that the card slot has 16 lanes. PCIe slots can be used to add GPU cards, RAID cards, Wi-Fi cards, and SSD cards.