Bar codes have specific symbology that is defined in the height and width of the bars as well as the spacing between the bars. Each of these bars might represent numeric data, alphanumeric data or character data, depending on the type of symbology being used.

Each bar code has a start bar and an end bar to allow the scanner to read the data precisely. Some bar codes have another bar before the end bar, known as the checksum bar code. After the scanner calculates the sum, it is verified with the value of the checksum bar code for accuracy. This ensures exact calculation with minimal errors.

Bar codes are read by scanners that are in fact photosensors used to convert the bars in the bar code into electrical signals as it is being scanned. Since the bars are distinguished by their width, height and spacing, they are then measured using software that recognizes and converts electrical signals from the bars into readable characters. The scanner software then transmits this data to the PC terminal. The whole process does not take more than a few seconds.

Bar code scanners are available in a variety of models. A few popular ones are the gun model, countertop model and portable variety. The simplest scanner model is connected to the PC and the keyboard. Software allows the scanner to read the bar code data and input it into the PC with minimal fuss. This is the most commonly used model, although the scanners that can be connected to serial ports or USB wedges are also popular. Since the data read in such cases does not interfere with the keyboard data, the software has complete control over the data flow from the scanner with little or no help manually.

Cordless scanners are also popular. Like cordless phones or cordless keyboards, these connect through radio waves with the base that is connected to the PC. This works similar to regular scanners, except that the data is first transmitted to the base and then sent to the system. These are usually short distance scanners, and they need to be within a specific range of the base to transmit the data accurately. Portable scanners are most useful when the user needs to input data simultaneously along with the scanning. This is especially true in cases when the user needs to go through menus to select the correct option. Almost all portable scanners come with a keyboard that the user can use to select the product.

All these scanners and many other models, such as the wireless ones, charge-coupled scanners, laser models, LED, handheld models, counter scanners, fixed-in-counter scanners and belt scanners, have the ability to store data regardless of the size and shape. The software used in these is basically the same, although a few changes might exist based on their utility. They decode the data in the bar code and store it for future reference.