The fundamental computer architecture in which the computer acts upon (executes) internally stored instructions. This enormous flexibility is why billions of computer CPUs are used for everything.
Read the Program
Before any data are processed, instructions are read into memory (RAM). The processing starts with the first instruction in the program, which is copied into a control unit circuit. The control unit executes the instructions sequentially until it finds one that causes it to break the sequence and go elsewhere in the program.
A CPU chip can handle billions of instructions per second, and as long as the instructions are valid and reference data within the program's boundaries, the control unit executes them. If not, the computer stops running the program (see abend
Input/output and processing are performed simultaneously. While data are being read or written, which is much slower than instruction execution, the operating system can direct the computer to process data in another program or for another user. See CPU
and von Neumann architecture