A hardware interface specifies the plugs, sockets, cables and electrical signals that pass through each line between the CPU and a peripheral device or communications network. The CPU socket on the motherboard determines which CPU chips can be used in the computer. Peripheral cards, such as a high-end graphics cards, plug into the bus on the motherboard. The most common buses are PCI and PCI Express. See PC data buses. The most widely used hardware interface for attaching external devices to computers is USB. It connects printers, cameras, music players, flash drives and auxiliary hard and optical drives. FireWire is also used for camcorders and hard disks. In addition, SATA is a common hard drive and optical drive interface. The GPIB IEEE 488 standard is used for process control instruments. See USB, SATA, GPIB and plugs and sockets. The de facto standard for connecting devices to local networks (LANs) is Ethernet, which is also used to hook up a cable or DSL modem. See Ethernet and standards.