Bar codes are those rows of black lines that seem to show up on everything from soup cans to library books to tracking labels on packages. Anytime there's a need to assign a very large number (more than about four or five digits) to identify something, it's usually easier to use a bar code instead of copying the number by hand. The familiar 8- or 12-digit bar code on most consumer products is called the Universal Product Code, or UPC.
A bar code reader is not standard equipment for most computer users, but they can be useful for things like inventory management or cataloging your collection of books, CDs and DVDs. The UPC Database Web site (http://www.upcdatabase.com/itemform.asp) can translate UPCs to the products that each UPC identifies.
Most bar codes use groups of vertical lines of different widths to indicate the binary value of each number or other character in the code. About a dozen different bar code structures exist, but it's possible to use the same readers (with different software) for just about all of them.
If you're interested in learning how to interpret many common bar codes, take a look at the Barcode Island Web site at http://www.barcodeisland.com/symbolgy.phtml.
A bar code reader is a light pen or laser that detects the thickness of each bar and converts the sequence back to a specific number, which it transmits to a computer. Depending on the size and shape of the object that carries the bar code, the person using a bar code reader might move a portable reader across the object, or he might move the object past a stationary reader. The computer searches for that number in a database that contains detailed information about the item assigned to that number, such as the name and price of the soup, the title of the book, or the shipping details of the package.
A bar code reader has two parts: a scanner that reads the bar code and converts it to electrical impulses, and a decoder that converts the signals from the scanner to a code number and transmits it to a computer.
Many older bar code readers use a wedge that plugs into a computer's keyboard socket and sends bar code numbers to the computer as key scans. Some wedges have a second keyboard connector, so it's possible to use both the bar code reader and a traditional keyboard or a 10-key keypad at the same time. Today, readers with a USB interface instead of a wedge are more common.
To use a bar code reader with your computer, simply plug the PS/2 cable from the wedge or the USB cable from the decoder into the appropriate connector on the computer and load the device driver software supplied with the reader. Once again, different makes and models of bar code readers have different feature sets, so the installation instructions and User's Guide are your best source of specific information.