A processor is the electronic circuitry within a computer that executes instructions that make up a computer program. The Processor performs basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions in the program. In most modern microprocessors the processor is contained on a single metal-oxide-semiconductor(MOS) integrated circuit(IC) chip. Some computers employ a multi-core processor, which is a single chip or "socket" containing two or more CPUs called "cores". The two main giants in the processor market are Intel and AMD.