You can break barcodes down into two different major groups: linear / one dimensional barcodes, and two dimensional barcodes. Two dimensional barcodes can pack a lot of data into a small space, but most inexpensive barcode scanners will not read them.

So if you need a bar code that is easy to print and can be read by virtually any scanner, you need a linear or one dimensional bar code. A linear bar code is composed of bars and spaces all in a single line. Linear bar codes can not hold a lot of data- typically no more than about 9 data characters for every inch of horizontal barcode space.

So what are the major types of linear barcodes and how do you choose the right one? A good web site that will help you pick the type of barcode you need is whichbarcode.com. They feature an interactive quiz that helps you select the right barcode. The major types of barcodes include:

• Bar Code 2/5 Interleaved- includes numbers only and you must use an even number of digits, optional checksum, variable length, may use bearer bars to prevent misreads, also handles ITF-14 barcodes.
• Bar Code 3/9- includes numbers, upper case letters, and a few special characters, optional checksum, variable length, Full ASCII mode possible with some barcode readers (at reduced density), often used by the DoD.
• Bar Code 93- includes numbers, upper case letters, and a few special characters, two required checksums, variable length, Full ASCII mode integrated into the barcode (at reduced density).
• Bar Code 128- includes all ASCII characters and offers a separate high density numeric mode, required checksum, variable length, also handles UCC/EAN 128, SCC-14, SSCC-18, and many other variants.
• Bookland- a special EAN 13 barcode with supplemental data used to turn ISBN book numbers into book barcodes with optional pricing information.
• Codabar- includes numbers and four letters which are used as the Start and Stop codes, used by libraries and blood banks.
• EAN 8- a fixed length 8 digit numeric bar code.
• EAN 13- a fixed length 13 digit numeric barcode used on retail products in Europe. All numbers are assigned by the EAN International.
• PostNet- a numeric bar code used by the US post office to route mail.
• UPC-A- a fixed length 12 digit numeric bar code used on all retail products in North America. All numbers are assigned by the Uniform Code Council.

 Why the misspelling? It seems the vast majority of people searching for information on bar codes misspell the word. Hence search engines think the proper spelling of “bar code” is “barcode”- because that’s what everyone is searching for.

 So, what is a barcode? A barcode is a way to display information in a way that machines, rather than humans, can easily read. The simplest barcodes are made up of a series of parallel vertical bars and spaces. These are called linear bar codes. The entire barcode is arranged in a line.

Barcodes must always start with a special character, called a Start Code. Every barcode must end with another special character called a Stop Code. The Start Code tells the barcode scanner to begin reading the barcode and it tells the barcode scanner what kind of barcode is to be read. The Stop Code tells the bar code scanner that it has reached the end of the barcode.

What do I mean by “kind” of barcode? Barcodes are like languages- there are lots of them. Each kind of barcode is designed to do something special. Many barcodes can only represent numbers. Some barcodes let you use portions or the entire ASCII character set. The most common barcode is the one you see on virtually every retail product in stores. It’s called a UPC barcode (Universal Product Code). UPC bar codes must have exactly 12 digits in them. You can not use anything other than numbers in a UPC barcode.

Another kind of barcode is Bar Code 3/9. (Also known as 3 of 9 or 39.)  Bar Code 3/9 lets you use numbers and upper case letters, plus a few special symbols. This type of barcode can be any length, although in practice they probably have at most 30 - 40 characters.

So to summarize, a barcode is a machine readable way of representing information. Some bar codes may show actual text below the barcode itself. This is called a human readable barcode. Some barcodes can only represent numbers, while others can include alphanumeric data. Most barcode scanners can read all linear barcodes. The are lots of different kinds of popular barcodes including: 2/5 Interleaved, 3 of 9, 93, 128, Codabar, EAN, Postnet, UPC, and more.

Further posts will describe the different kinds of bar codes, what you can not do with a bar code, how scanners work, and much more.