A USB expansion card is used to provide extra connection ports to a computer. USB stands for Universal Serial Bus. It is the most common type of port found on computers. Peripherals such as printers, keyboards, printers, removable flash drives and mouse are connected to the USB ports. Normally, a modern motherboard commonly has at least two USB slots. Some of the advantages of USB are hot-plugging and up to 127 USB devices can share a single system resource. USB has width of 1-bit due to its serial nature. They can be plugged into PCI, PCIe, or PCMCIA slots.