During the functioning of a computer. The first stage (things to work upon) is called input stage, the second stage (the actual work being performed) is called process stage and the third stage (the result) is called output stage. Certain input is needed to accomplish a task, a process is carried out on the input to obtain the output.
Every task follows this Input-Process-Output cycle (IPO cycle in short). A computer follows the I-P-O cycle that is; it needs certain input, carries out a process and produces the output.