Types of USB Connectors
Currently, there are four types of USB connectors: Type A, Type B, mini-A and mini-B and are supported by the different USB specifications (USB 1, USB 2 and USB-OTG).

Type A (Host)
Often referred to as the downstream connector, the Type A USB connector is rectangular in shape and is the one you use to plug into the CPU or USB hub.

Type B (Device)
Also called the upstream connector, the Type B USB connector is more box-shaped and is the end that attaches directly to the device (such as a printer or digital camera).

USB 1.1 specifies the Type A and Type B.

Mini-B
The USB 2.0 connector was too large for many of the new handheld devices, such as PDAs and cell phones. The mini-B was introduced to enable consumers to take advantage of USB PC connectivity for these smaller devices.

USB 2.0 specifies the Type A, Type B and mini-B.

Mini-A
With the need to connect mobile devices without the aid of a computer, the mini-A port was designed to connect the new generation of smaller mobile devices.

USB OTG specifies the mini-A.

USB 1x
First released in 1996, the original USB 1.0 standard offered data rates of 1.5 Mbps. The USB 1.1 standard followed with two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much less bandwidth.

USB 2x
In 2002 a newer specification USB 2.0, also called Hi-Speed USB 2.0, was introduced. It increased the data transfer rate for PC to USB device to 480 Mbps, which is 40 times faster than the USB 1.1 specification. With the increased bandwidth, high throughput peripherals such as digital cameras, CD burners and video equipment could now be connected with USB. It also allowed for multiple high-speed devices to run simultaneously. Another important feature of USB 2.0 is that it supports Windows XP through Windows update.

Different types of USB connectors from left to right ♦ Mini-A plug ♦ Mini-B plug ♦ B-type plug ♦ A-type receptacle ♦ A-type plug	Pin configuration of the USB connectors Standard A/B, viewed from face of plug

Sources

• http://en.wikipedia.org/wiki/USB
• http://www.webopedia.com/DidYouKnow/Computer_Science/2005/usb.asp