The USB cable is a standard accessory included with every computer or peripheral device sold today. Most computer users are familiar with the common rectangular USB connector, but there are others that have different shapes which are less well known. It is also easy to mistake a FireWire connector for a USB connector since both of them are rectangular. Consumers who can identify the subtle differences between the various connectors are less likely to make this frustrating mistake when purchasing computer equipment.
USB stands for Universal Serial Bus. It is used to connect all kinds of peripheral devices to a computer including keyboards, mice, printers, scanners, and tablets. A serial bus transmits data one bit at a time, unlike a parallel bus that transmits several bits simultaneously. USB is significantly faster than the older serial and parallel ports that can still be found on computers today. Devices are linked together in series using hubs. Each host can support up to 127 devices including hubs.
The most common USB connector is the USB-A, also known as the Standard-A. It is used for flash drives and the cables of most peripheral devices. The USB-A is the largest of all the connectors and has a slim rectangular cross-section. Inside the metal cover is an insulator with four pins mounted in a row. The outer two pins carry the power and the inner two pins carry the signal. The socket has a large tab inside it that prevents the connector from being installed upside down. It can be difficult to see the tab so the general rule is to plug the connector in with the USB trident symbol facing upwards.
The other main USB connector is the USB-B, also known as the Standard-B. It is used for devices that have a removable cable. The USB-B has a square cross-section with beveled top corners. Inside the plug, two pins are mounted on both the upper and lower insulators. While the USB-A is meant to receive power from an upstream device, the USB-B is meant to provide power to a downstream device. The different shapes prevent one connector from being plugged into another.
Some devices are not large enough to use the standard USB connector. These include digital cameras, music players, mobile phones, memory card readers, and personal digital assistants. These devices use micro and mini connectors which are half the height of a standard connector. The micro connector is half the width of the mini connector. They have five pins instead of four, with the additional pin being for identification purposes. Both the mini and micro connectors have A and B types like the standard connector to avoid confusion when connecting devices.
The maximum length of a USB cable is only five meters. This is because the USB standard specifies a very fast response from the devices connected to it. This is short compared to the maximum length of one hundred meters for thin Ethernet cables. It is possible to link USB hubs together and extend the overall length but not by much. IT is because of this limit that computers are not usually networked together with USB cables, unless they are very close together or there are no Ethernet ports available. It is more common to use USB wireless adapters for networking.
FireWire is a brand name for a high speed serial bus used for connecting peripheral devices to a computer. The standard USB connector and the FireWire connector look similar and are both rectangular but FireWire has beveled edges on one side. They also have different logos and a different number of pins inside the connector. Most new computers sold today support both USB and FireWire but there are still many older computers that only support USB. The high speed of FireWire is not essential for most peripheral devices and the USB models work just as well.