In computing, a processor or processing unit is a digital circuit which performs operations on some external data source, usually memory or some other data stream. It typically takes the form of a microprocessor, which can be implemented on a single metal–oxide–semiconductor integrated circuit chip; in the past, processors were constructed using multiple individual vacuum tubes, multiple individual transistors, or multiple integrated circuits.
The term is frequently used to refer to the central processing unit in a system. However, it can also refer to other co-processors.
Traditional processors are typically based on silicon, however, researchers have developed experimental processors based on alternative materials such as carbon nanotubes, graphene, and alloys made of elements from groups three and five of the periodic table. Further, transistors made out of a single sheet of silicon atoms one atom tall and other 2D materials have been researched for use in processors.
The progress of processors has followed Moore's law closely, the theory that the number of transistors in processors will double every two years.
Photonic processors are based on using light to make computations instead of semiconducting electronics. Processing is done by photodetectors sensing light produced by lasers inside the processor.