In data processing or information processing, a Data Processor or Data Processing Unit or Data Processing System is a system which processes data which has been captured and encoded in a format recognizable by the data processing system or has been created and stored by another unit of an information processing system.

A data processor is a specialized component or form of an information processing (sub)system. Its chief difference is that it tends to perform a dedicated function (i.e., its program is not readily changeable). Its dedicated function is normally to perform some (intermediate) step of converting input ('raw' or unprocessed) data, or semi-processed information, in one form into a further or final form of information through a process called decoding / encoding or formatting or re-formatting or translation or data conversion before the information can be output from the data processor to a further step in the information processing system.

For the hardware data processing system, this information may be used to change the sequential states of a (hardware) machine called a computer. In all essential aspects, the hardware data processing unit is indistinguishable from a computer's central processing unit (CPU), i.e. the hardware data processing unit is just a dedicated computer. However, the hardware data processing unit is normally dedicated to the specific computer application of format translation.

A software code compiler (e.g., for Fortran or Algol) is an example of a software data processing system. The software data processing system makes use of a (general purpose) computer in order to complete its functions. A software data processing system is normally a standalone unit of software, in that its output can be directed to any number of other (not necessarily as yet identified) information processing (sub)systems.