The fundamental computer architecture in which the computer acts upon (executes) instructions temporarily stored internally in its memory (RAM). This flexibility is why computers are used for an endless number of operations. However, with appliances, sensors and myriad other electronic devices dedicated to only one set of tasks, a single program is generally stored permanently.
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 a go-to or jump instruction 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. Otherwise, the computer stops running the program (see
abend).
Operations Overlap
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
double buffering,
CPU and
von Neumann architecture.