I think we use the real-time system only when we have to do multi task within a certain time. I think the ATM machine is a real-time system because it also works for a certain time. The time to enter the password is also fixed. If you do not enter the password within a certain time then the process starts from beginning If you do not take money for a certain amount of time then money goes back into machine. Is ATM machine work on RTOS ?