Universal Serial Bus

USB is an external bus allowing you to connect external peripherals to your PC such as mice, keyboards, digital cameras, external hard disk drives, external CD recorders, printers, scanners, etc. There are two versions available: 1.1 and 2.0. USB 1.1 has a maximum transfer rate of 12 Mbps (around 1.5 MB/s), while USB 2.0 has a maximum transfer rate of 480 Mbps (around 60 MB/s). Since around 1998 all PCs come with USB ports on the motherboard. To each USB port it is possible to connect up to 127 peripherals.

The most common USB plugs are “Type A”, used on the USB ports located on the PC, and “Type B”, located on peripherals such as printers and scanners. Smaller devices, like digital cameras, use smaller plugs, usually proprietary (i.e. without any standardization and with a layout and pinout that depends on the peripheral make and model).

click to enlarge
Figure 1: USB ports on a motherboard.

click to enlarge
Figure 2: Standard USB plugs.