The IPOS Cycle

The IPOS cycle represents the four basic tasks of any computer:

• input : Input is obtaining data from the outside world and delivering it to one or more components in the computer.
• processing : Processing is the execution of one or more computer programs on the data. Processes can vary greatly in size, complexity, and function,  i.e. Processes will often perform mathematical operations, string operations, computer graphics, storage operations, and/or operating system activities.
• output : Output is taking information stored in the computer and
  delivering it to the outside world, usually for humans to view.You might think of input as the raw data for a process and output as the results of the process.
• storage : Storage is applied today to both data and program code. Storage usually refers to secondary storage, that is, the permanent placement of information on a device like a disk, but it can also refer to temporary storage in some form of memory such as main memory (RAM) or short-term storage such as registers and cache.

The IPOS cycle

 Although a computer will do all four of these, it is not necessarily the case that all four of them are done in this sequence. For instance, a program may require some input followed by processing followed by additional input followed by more processing.
Also, results from a process can either be output or stored in a file, thus omitting either output or storage.

Resources

Linux with Operating System Concepts by Richard Fox