USB

Just about any computer that you buy today comes with one or more Universal Serial Bus connectors. These USB connectors let you attach mice, printers and other accessories to your computer quickly and easily. The operating system supports USB as well, so the installation of the device drivers is quick and easy, too. Compared to other ways of connecting devices to your computer (including parallel ports, serial ports and special cards that you install inside the computer's case), USB devices are incredibly simple.

­In this article, we'll look at USB ports from both a user and a technical standpoint. You'll learn why the USB system is so flexible and how it's able to support so many devices so easily -- it's truly an amazing system.

Anyone who has been around computers for a while knows the problem that the Universal Serial Bus is trying to solve -- in the past, connecting devices to computers has been a real headache.

Printers connected to parallel printer ports, and most computers only came with one. Things like external storage media, which need a high-speed connection into the computer, would use the parallel port as well, often with limited success and not much speed.
Modems used the serial port, but so did some printers and a variety of odd things like personal digital assistants (PDAs) and digital cameras. Most computers had at most two serial ports, and they were very slow in most cases.
Devices that needed faster connections came with their own cards, which had to fit in a card slot inside the computer's case. Unfortunately, the number of card slots is limited and some of the cards are difficult to install.

The goal of USB is to end all of these headaches. The Universal Serial Bus gives you a single, standardized, easy-to-use way to connect up to 127 devices to a computer.

Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes:

Printers
Scanners
Mice
Joysticks
Flight yokes
Digital cameras
Webcams
Scientific data acquisition devices
Modems
Speakers
Telephones
Video phones
Storage devices
Network connections

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.