The Decoders are an essential part of an Bar Code system, they would can be defined the heart of the system, the decoder must not to mistake, it has to do the necessary controls to interpret the Bar Code and have to be quick and reliable.
For many applications, now, the Readers  have integrated the decoder and make up an one and compact device, in this section we talk of the external Decoders at the readers that add some options and features that became essential for hardware integration.