into the memory of a device to control computations was invented by Charles Babbage as part of his difference engine.

Computer software has to be loaded into the computer's storage device. Once the software is loaded, the computer is able to execute the software. Computers operate by executing the computer program. This involves passing instructions from the application software, through the system software, to the hardware which ultimately receives the instruction as machine code. Each instruction causes the computer to carry out an operation such as moving data, carrying out a computation, or altering the control flow of instructions.

Data movement is typically from one place in memory to another. Sometimes it involves moving data between memory and registers which enable high speed data access in the CPU. Moving data, especially large amounts of it, can be costly. So, this is sometimes avoided by using pointers to data instead. Computations include simple operations such as incrementing the value of a variable data element. More complex computations may involve many operations and data elements together. Instructions may be performed sequentially, conditionally, or iteratively. Sequential instructions are those operations that are performed one after another. Conditional instructions are performed such that different sets of instructions execute depending on the value of some data. In some languages this is know as an, if, statement. Iterative instructions are performed repetitively and may depend on some data value. This is sometimes called a loop. Often, one instruction may call another set of instructions that are defined in some other program or module. When more than one computer processor is used, instructions may be executed simultaneously.

A simple example of the way software operates is what happens when a user selects an entry such as copy from a menu. In this case, a conditional instruction is executed to copy text from data in a document area residing in memory, perhaps to an intermediate storage area known as a clipboard data area. If a different menu entry such as paste is chosen, the software may execute the instructions to copy the text from the clipboard data area to a specific location in the same or another document in memory.


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