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USB

The Universal Serial Bus (USB) is a contemporary communication standard developed by the computer and telecommunication industries.  It has replaced many of the special interfaces such as conventional serial ports, parallel ports, and keyboard ports. Most new PCs and Macs have USB connectors and the number of USB-connected peripherals has increased exponentially over the last 30 years.  USB provides power to the devices connected to it.  USB 1.1  provides 12 Mbit/s and 1.5 Mbit/s data transmission speeds. USB can't be used directly as a fast connection between PCs, but there are special products which allow small scale networking using USB bus.  USB provides a powerful, hot-plug-capable, "true plug-and-play" interface between a host computer and add-on peripheral devices.

NOTE - "Hot-plug-capable" means that you can plug in, use, and unplug devices without having to shut down the host computer.

These devices can be just about anything: keyboards, mice, joysticks, telephones, scanners, printers, security dongles, microphones, speakers, floppy drives, cameras, modems, CD-ROM drives, etc.

USB was designed to improve on earlier peripheral connection technologies.   USB allows end-users to connect peripheral devices to a host computer on the fly, without having the user hassle with:

Shutting down/restarting the computer (a big plus!)
Opening the computer case
Installing a card
ID conflicts
Termination
Loading device drivers (although some devices may require a one-time driver installation).

In addition, USB provides:

A "tiered-star hub" network topology, allowing for the connection of up to 127 devices per host computer
Simple, standardized plugs for the broad range of devices
Power for some devices directly through the USB cable
Support for a variety of data rates, from 1.5 Mbps to 120 Gbps.
Automatic loading and unloading of device drivers as needed

USB devices use several different kinds of plugs, starting with Type A and Type B:

USB cables

The Type A plug (left): connects to the host computer or an upstream hub.
The Type B plug (right): connects downstream to the USB device. It's "kind of house-shaped."  Some devices (like a mouse) have the cable soldered into the device, and therefore don't use this connector.
NOTE - "Upstream" means moving up the device chain, in the direction of the host computer. "Downstream" means moving down the device chain, away from the host computer, as shown in the following figure.


USB network. Picture courtesy Apple

In USB 1.1, high speed connections (12 Mbps) use shielded cabling to reduce interference at higher connection rates, while low speed connections (1.5 Mbps) may not. 
Each connector has four pins, two for power and two for data.

 

Here are a few links to more info about USB:

www.usb.org - The official USB technology forum home page.
USB Central - Jan Axelson's page of USB info and links. (Jan also has an excellent book on USB - check it out.)
Linux USB - good source of info about USB support under Linux.
USB Architecture and Driver Support     - from Microsoft
USB Stuff - a company which sells USB equipment and has USB news on its web site.

 

 

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This site last updated 7/11/2008