USB connectors are used with Universal(通用的) Serial(一連串的) Bus(匯流排) (USB) standard(規格 標準) ports. USB is an external(外部) bus standard that supports data(數據資料) transfer(轉換) rates(比率) of 12 Mbps(兆位/秒-電腦資料率) in its version 1.1 and 480Mbps in its version(版本) 2.0. A single USB port can be used to connect up to 127 peripheral(周邊設備) devices(設備), including mice(滑鼠), modems(數據機), and keyboards. USB also supports(支持) Plug-and-Play(隨插即用) installation(安裝) and hot plugging(熱插拔). USB 2.0 connectors are the “glue”(黏著劑) that holds these systems together, allowing them to transfer, receive(接收) and translate(翻譯) data.

The USB connector types can be used to connect USB products to other USB products or they can be used to connect USB wires and peripherals to other standard port types.

註: 熱插拔（Hot swapping 或 Hot plugging）即「帶電插拔」，指可以在電腦運作時插上或拔除硬件。配合適當的軟件，便可以在不用關閉電源的情況下插入或拔除支援熱插拔的周邊裝置，不會導致主機或周邊裝置燒燬並且能夠即時偵測及使用新的裝置。相比隨插即用（Plug-and-Play），熱插拔對軟硬件的要求還包含了電源，信號與接地線的接觸順序。

Some styles of USB connectors can be mounted(架設好的) directly(直接) into PC boards(板).  These USB are among(在….之中) the most commonly(ㄧ般的) used types of USB connectors and are often referred to(被稱為) as USB motherboard(主機板) connectors or internal(內部的) USB connectors.  The drawback(缺點) to this style of connector is that it takes up(佔用) space on the PC board and requires(需要) either drilled holes or perform(預先形成) slots into which it can be mounted(架設好的). The other common mounting(裝備) style is surface(表面) mounting.  Unlike PC mount(底座) connectors, mount panel(控制板) USB connectors do not require drilled holes in the PC board.  They are attached to(附屬於) the PC board traces by soldering(焊料.接合物).  For the most part, this style is attached to the front of the PC board and is alternately(交替地) referred to as USB front panel(控電板) connectors or simply front USB connectors.  Straight and right angle connectors are also available(可用的).  As with most connector types, USB connectors are available with either male or female plugs.   Specific(特殊的) male-to-male or female-to-female adapters(轉接器) are also available, but may require custom(訂做的) manufacture

History

The USB 1.0 specification model was introduced in November 1995. USB was created by the Core(中心部份) group of companies that consisted of(組成) Intel, Compaq, Microsoft, Digital, IBM, and Northern Telecom. Intel produced the UHCI host controller and open software stack; Microsoft produced a USB software stack for Windows and co-authored the OHCI host controller specification with National Semicondutor and Compaq; Philips produced early USB-Audio; and TI produced the most widely used hub chips. Originally USB was intended to replace the multitude of connectors at the back of PCs, as well as to simplify software configuration of communication devices.

As of 2008, the USB specification is at version 2.0 (with revisions). Hewlett-Packard, Intel, Lucent (now LSI Corporation since its merger with Lucent spinoff Agere Systems), Microsoft, NEC, and Philips jointly led the initiative(首創精神) to develop a higher data transfer rate than the 1.1 specification. The USB 2.0 specification was released(發表) in April 2000 and was standardized by the USB-IF at the end of 2001. Equipment conforming with any version of the standard will also work with devices designed to any previous specification (known as backward compatibility).

Smaller USB plugs and receptacles for use in handheld and mobile devices, called Mini-B, were added to USB specification in the first engineering change notice. A new variant of smaller USB plugs and receptacles, Micro-USB, was announced by the USB Implementers Forum on January 4, 2007.

USB signaling

USB supports three data rates:

A Low Speed (1.1, 2.0) rate of 1.5 Mbit/s (187.5 kB/s) that is mostly used for Human Interface Devices (HID) such as keyboards, mice, and joysticks.

A Full Speed (1.1, 2.0) rate of 12 Mbit/s (1.5 MB/s). Full Speed was the fastest rate before the USB 2.0 specification and many devices fall back to Full Speed. Full Speed devices divide the USB bandwidth between them in a first-come first-served basis and it is not uncommon to run out of bandwidth with several isochronous devices. All USB hubs support Full Speed.

A High-Speed (2.0) rate of 480 Mbit/s (60 MB/s).

Types of USB connector

There are several types of USB connectors, including some that have been added as the specification has progressed. The original USB specification detailed Standard-A and Standard-B plugs and receptacles. The first engineering change notice to the USB 2.0 specification added Mini-B plugs and receptacles.

The Standard-A type of USB connectors takes on the appearance of flattened rectangles. This kind of connector is most frequently seen on cables that are permanently attached to a device, such as one on a cable that connects a keyboard or mouse to the computer. Standard-B connectors looks square with beveled corners, and plugs into upstream sockets on devices and hubs. The Standard-B connector is mainly used only for the device end of a removable cable, such as between a hub and a printer. This two-connector scheme prevents a user from accidentally creating a loop.

The non-standard Mini-USB's, official Mini-B, Micro-A, and Micro-B connectors are used for smaller devices such as PDAs, mobile phones or digital cameras. The Standard-A plug is approximately 4 by 12 mm, the Standard-B approximately 7 by 8 mm, and the Mini-A and Mini-B plugs approximately 2 by 7 mm.

The Micro-USB connector, was announced by the USB-IF on January 4, 2007 .It is intended to replace the Mini-USB plugs used in many new smartphones and Personal digital assistants. It is about half the height of the mini-USB connector, but features a similar width.