Broadly speaking, there are 2 types of bar codes in use today, one-dimensional bar code and 2-dimensional bar code. 1-D is by far the more common. A 1-D bar code appears on nearly every item you purchase at a supermarket. It is what enables you to perform self-checkout at The Home Depot. Every item at your drugstore bears a 1-D bar code. 1-D bar codes appear as a series of black bars representing numbers.