Bar codes, such as the familiar U.P.C. symbol used for point-of-sale, are physical marks arranged in a "linear" manner of dark and light "bars" (hence the term "bar" code). Bar codes are designed to provide reliable encodation of limited amounts of data (typically 30 characters maximum).

Bar Code Advantages:

• Inexpensive and easy to produce (can be disposable)
• Easily read
• Can be very durable
• Wide use and acceptance
• Public domain / ANSI, CEN and ISO/IEC standards
• Extended read range available (up to 20 ft.)
• Can be read at high speed (up to 3500 fpm)
• Large choice of printing and reading equipment
• High accuracy

Bar Code Limitations:

• Require line-of-sight to read
• Can be damaged by common contaminants or abrasion
• Limited data capacity
• Read-only.

Bar Code Standards

Technical specifications are well established for bar code symbologies. Application standards have also been developed by a large number of industries for using bar codes on shipping labels, hospital items, parts, point-of-sale, and other uses. ANSI, the Commission for European Normalisation (CEN) and ISO/IEC have issued technical specifications and application standards for bar code use.

2D Symbols

Stacked bar codes and matrix symbols are also physical marks but are arranged in two dimensions. They can contain much more information than conventional bar code symbols and many can be printed small enough to identify electronic components. All have error detection features; some stacked bar codes and all matrix symbologies have user-selectable levels of erasure correction capabilities. PDF 417 is the most commonly-used stacked bar code. DataMatrix and MaxiCode (formerly UPScode) are the most commonly-used matrix symbologies. QR Code is gaining acceptance in some areas.

2D symbologies are designed to:

• Efficiently convey large amounts of data,
• Provide identification of items too small for conventional bar codes, and
• Require less label space than conventional bar codes.

Stacked Bar Codes, as the term suggests, are based on linear bar codes with varying width bars and spaces. Thin "slices" of a bar code are stacked to create the complete symbol. Additional coding within the symbol indicate the location of each piece of data to ensure correct decoding.

Matrix Symbols, bar codes, use regularly-shaped "cells" to encode data. Cells are all the same size and shape within a given symbol. As a result, reading equipment is not concerned with the edges of the cell, just whether its center is dark or light. Because readers do not have to determine edge location, contrast and print quality may be less critical than with bar codes.

2D Symbology Advantages:

• High data density / small size,
• Multi-language capabilities,
• Public domain status of most symbologies,
• ISO/IEC standards for common symbologies,
• Technology and applications have been or are being standardized,
• Near-contact to long-range (approximately 3 meters) reading,
• Growing use and acceptance,
• Support by multiple equipment and software suppliers,
• Inexpensive and relatively easy to produce (disposable),
• Increased data integrity (error and erasure correction),
• Include data reconstruction algorithms to retrieve data from badly damaged symbols,
• High reliability, and
• Omnidirectional reading (typically).

Stacked Bar Codes Only:

• Can be read with (properly programmed) existing laser scanners,
• May be easier to implement (than matrix symbologies) in existing bar code programs.

Matrix Symbolologies Only:

• Poor quality, damaged and low contrast symbols may be easier to read,
• All matrix symbologies omnidirectionally readable.

2D Symbology Limitations

• Line-of-sight required,
• Not as well understood as linear bar code,
• Can be damaged by common contaminants or abrasion,
• Read only.

Stacked Bar Codes Only:

• Not all readers can read stacked bar codes omnidirectionally.

Matrix Symbolologies Only:

• Cannot be read with moving beam laser readers

2D Symbology Standards:

• ANSI, CEN and ISO/IEC have issued or are finalizing symbology specifications for commonly-used symbologies. AIM Global has issued specification for a few additional symbologies.