A Universal Serial Bus (USB) Cable is primarily used to connect a USB device to a host. Common hosts include computers and video game consoles. While there are multiple USB standards, cables that are fully compliant with USB 1.1 specifications will work with USB 2.0 technology and vice versa. USB cables can be identified by the USB trident on top of the plug overmolds of type “A” and “B” connectors.
A USB cable can have numerous types of plug ends, the style of which is called a connector. Connector types include Standard-A, Standard-B, Mini-B, Micro-A, Micro-B, and Micro-AB. These plugs go into corresponding receptacles built into hosts and devices. Standard-A receptacles are the type commonly referred to as USB ports on computers; Standard-B receptacles are usually found on large peripheral devices such as printers and scanners; Mini and micro receptacles are usually on small devices like digital cameras and cellular phones; Mini-AB receptacle are, according to the standard, only on USB On-The-Go devices. Most USB cables that connect a device to a computer will have a Standard-A plug on one end and another type of plug on the other.
Beyond connector types, compliant USB cables are not proprietary. A standard cable can connect a device to a Macintosh or a Windows PC, for example. The software within the device, however, may not work with the host. In addition, some companies create cables that appear similar to USB cables but are not compliant with USB standards — such connectors should not have the trident logo on them.
A standard USB cable contains multiple wires. One wire contains a path for a five volt (5V±5%) power supply; two are twisted-pair data wires; and one is a ground.
A USB cable under 2.0 specs can only be five meters (roughly 16.4 feet) long. This limit was established due to a cable delay spec of 26 nanoseconds, which allows for reflections to settle at the transmitter before the next bit is sent. USB hosts must have their commands answered within an allowed time frame or they will consider the commands lost — cables significantly longer than five meters would result in too much of a delay.
There are many solutions for connecting USB devices beyond the 5 meter cable limit. These solutions include using extender cables, which are self-powered hubs with a fixed 10 meter cable and a one-port bus powered hub in the middle; using up to five hubs in a chain; and building a bridge that acts as a USB device on one side and has a host controller at the other end. It's best to use a long-haul signaling protocol like Ethernet or RS-485 in the middle if this method is used.
