The processor chip or central processing unit (CPU) is the brains of the computer. It is an electronic circuit that processes commands and executes programs. The basic operation of the processor chip is to execute a series of instructions. These instructions are stored in memory and are called programs. The sequence of instructions from the program are read into computer memory and are then processed sequentially by the processor. All of the instructions are represented by a series of numbers in binary code.
There are four steps that processors use to run the program’s instructions. These are fetch, decode, execute and write. In fetch, the processor reads the instruction from memory or from a storage device. In the next step, the processor decodes the instruction so that it and other parts of the computer can understand it. Next the processor chip executes the instructions, and finally writes the results of the execution back into some form of memory. At that point, the entire process repeats itself at a very high speed, depending on the clock rate of the processor. This is measured in Hertz. In the beginning of PCs, this was measured in tens of megahertz, but is now measured in multiple gigahertz.
Many modern computers have multiple processor chips which can run in parallel to improve processing speeds even further. This design allows the instructions to be split up so that one processor can be fetching and decoding before the previous instruction completes execution and writing.