central processing unit


A central processing unit (CPU), also referred to as a central processor unit, is the hardware within a computer that carries out the instructions of a computer program by performing the basic arithmetical, logical, and input/output operations of the system. The term has been in use in the computer industry at least since the early 1960s. The form, design, and implementation of CPUs have changed over the course of their history, but their fundamental operation remains much the same.

A computer can have more than one CPU; this is called multiprocessing. Some integrated circuits (ICs) can contain multiple CPUs on a single chip; those ICs are called multi-core processors.

Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical operations, and the control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

Not all computational systems rely on a central processing unit. An array processor or vector processor has multiple parallel computing elements, with no one unit considered the "center". In the distributed computing model, problems are solved by a distributed interconnected set of processors.


When the 1970s dawned, computers were still monster machines hidden in air-conditioned rooms and attended to by technicians in white lab coats. One component of a mainframe computer, as they were known, was the CPU, or Central Processing Unit. This was a steel cabinet bigger than a refrigerator full of circuit boards crowded with transistors.

Computers had only recently been converted from vacuum tubes to transistors and only the very latest machines used primitive integrated circuits where a few transistors were gathered in one package. That means the CPU was a big pile of equipment. The thought that the CPU could be reduced to a chip of silicon the size of your fingernail was the stuff of science fiction.

In the '40s, mathematicians John Von Neumann, J. Presper Eckert and John Mauchly came up with the concept of the stored instruction digital computer. Before then, computers were programmed by rewiring their circuits to perform a certain calculation over and over. By having a memory and storing a set of instructions that can be performed over and over, as well as logic to vary the path of instruction, execution programmable computers were possible.

The component of the computer that fetches the instructions and data from the memory and carries out the instructions in the form of data manipulation and numerical calculations is called the CPU. It’s central because all the memory and the input/output devices must connect to the CPU, so it’s only natural to keep the cables short to put the CPU in the middle. It does all the instruction execution and number calculations so it’s called the Processing Unit.

The CPU has a program counter that points to the next instruction to be executed. It goes through a cycle where it retrieves, from memory, the instructions in the program counter. It then retrieves the required data from memory, performs the calculation indicated by the instruction and stores the result. The program counter is incremented to point to the next instruction and the cycle starts all over.