A computer's processor is the control center for the computer, and it carries out the computations that allow the computer to function. The circuits in this central processing unit (or CPU) send commands to the other components of the computer to run programs, accept input and produce output.
The CPU retrieves information from the computer's memory and conducts operations on that information. The CPU thus operates like the working memory of a person's brain; it takes information from long-term storage when it is needed for immediate processing. In this way, the CPU operates as a general-purpose information processor, which can accommodate different types of information from other parts of the computer.
Every computer has a processor, but the exact type of processor varies between different computers. Macs and PCs use different CPUs, and there are various manufacturers of processors for each system. Some systems run parallel processors, which allow multiple operations to run simultaneously.
The operations in the processor are simple binary computations using electrical circuits. These computations are carried out extremely quickly; a standard computer's processor can carry out millions of calculations per second, while supercomputers reach into billions of computations per second. However, most programs require a massive number of such calculations to carry out, which is why computer operations do not operate instantaneously.