The USB (Universal Serial Bus) specification provides a platform to allow a single USB port to drive 127 USB peripherals from a single host termination (PC). USB also allows remote powering from the host of a broad range of low power after-market accessories including travel lights, mobile phone chargers and laptop backup hard drives not requiring their own power supplies.
USB 1.1 provided data transfer rates of up to 12 Mbps. The latest specification, USB 2.0, provides for data transfer rates up to 480 Mbps. USB 2.0 uses the standard A-plug that connects to the host and standard B-plug that fits into the peripheral. As these are too large for many portable units, mini A-plug and B-plugs are commonly used.
The latest USB OTG (On The Go) allows peripheral equipment (PDAs, digital cameras and mobile phones) to communicate with each other.
For example, USB OTG allows digital cameras to send files directly to a printer without the use of a computer. Equipment with USB OTG has the ability to be either a host or a peripheral and can dynamically switch between the two.
Equipment with USB OTG capability has smaller interface sockets. The connector can take either mini A-plugs or mini B-plugs and is called a mini-AB receptacle.
Read more Here