Assuming that a program that serves to make any (for example, 3 and 5), the sum of two integers is hard a PC saved to disk if someone wants to make a sum with this programme, must follow, as a minimum, the following five steps: 1. turn on the computer. Then some programs of the operating system installed on the machine will be loaded into main memory and take control of the computer, which will be waiting that the user say what you want done. 2. Select Add program to run it. If the operating system provides a graphical interface, the user can select the program by double clicking with the mouse on its name (add).
But, on the assumption that the interface is text mode, also called command line mode, then the user must write their name and press the Enter key. In either of the two cases, the operating system will search for that program on the hard disk and, if found, load it into memory, i.e. in it You will write a copy of the instructions of the program added. Immediately later, the control unit will read and interpret these instructions, one at a time, to run as well. Two of the first instructions will ask the user numbers that it wished. So, the implementation of the programme stops, on both occasions, pending that the user type in those numbers. 3. Insert the input data.
The user must type a number (for example, 3) and press the Enter button, and perform the same operation for the second number (for example, 5). Then the arithmetic/logic unit will calculate the sum, which in this case will be 8. The three data is also saved in the memory. Subsequently, the result of calculating the sum of the two input numbers is displayed by the monitor screen, where the user may see something like: Welcome to the program that PERFORMS sums whole enter the first number (integer): 3. Insert the second number (integer): 5 the sum is: 8 press any key to exit. In the course of implementing this programme, the user intervenes twice, both to write the numbers that you want to add. Somehow, there has been a dialogue between the user and the machine, or put another way, to run this program from beginning to end, is necessary that the user involved at any given time. Such programs are called interactive. Video games are excellent examples of interactive programs, since, in them, the user interacts constantly with the machine. 4 End the program. At this point, the add program will end once the user press any key. Consequently, the operating system will release the memory space occupied by the instructions of the program and all data used in his execution (in this case three data). After executing any program always there to free occupied memory space and, thus, hollow to allow other programs to run. 5. Switch off the computer. If now the user decides to shut down the computer, you will also release the memory space occupied by the programs of the operating system and everything will be at the beginning. Roughly, this is what happens when running the program added. In explaining many technical details have been overlooked. However, note that, all major units of the computer have been involved in the process.