The concept of multitasking is critical to modern operating systems. Users depend on the ability to run more than one program at a time. This ability requires some extra work on the part of the operating system. Any operating system needs to have a way to keep track of which programs are currently open (meaning loaded into memory) and which one is ACTIVE. Only one program at a time is active. The active program is the one that is currently getting your attention. Usually the active program looks like it is in front of the others on the screen. It might overlap other programs that are visible in the background. An active program usually also has a different colored caption than other programs. Any program that is visible is open, but may not be the active program. Any multitasking operating system will have ways to switch between active programs and some way of determining which programs are active and which are open.