How USB Ports Work

USB Cables and Connectors
The rectangular socket is a typical USB socket.
The rectangular socket is a typical USB socket.

Connecting a USB device to a computer is simple -- you find the USB connector on the back of your machine and plug the USB connector into it.

If it's a new device, the operating system auto-detects it and asks for the driver disk. If the device has already been installed, the computer activates it and starts talking to it. USB devices can be connected and disconnected at any time.

A typical USB connector, called an "A" connection

Many USB devices come with their own built-in cable, and the cable has an "A" connection on it. If not, then the device has a socket on it that accepts a USB "B" connector.

A typical "B" connection

The USB standard uses "A" and "B" connectors to avoid confusion:

  • "A" connectors head "upstream" toward the computer.
  • "B" connectors head "downstream" and connect to individual devices.

By using different connectors on the upstream and downstream end, it's impossible to ever get confused -- if you connect any USB cable's "B" connector into a device, you know that it'll work. Similarly, you can plug any "A" connector into any "A" socket and know that it'll work.

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