Operating Systems have normally 4 types; Ii is based on the types of system they control and what kind of applications they support. The types are:

• RTOS (Real-time operating system) -It is used to control machinery, scientific tools and industrial devices. An RTOS normally has small user-interface capacity, and no end-user programs. A key part of an RTOS is managing the sources of the PC so that particular operations run in exactly same time, each time this is happen. In a difficult machine, having a part move more rapidly just because system sources are available may be just as disastrous as having it not move at all because the system is busy.

• Single-user, single task - this OS is planned to help the system in order that one user can efficiently do one thing at a time. The Palm OS for Palm handheld computers is a best example of a modern single-user, single-task OS.

• Single-user, multi-tasking – Most of the user in world are use this type of OS. Microsoft's Windows and Apple's MacOS are examples of OS that will allow a single user have different programs do same time. For example, it's possible for user to be writing a note in a word pad while downloading a file from the net while scans the photo.

• Multi-user -It is allows many different users to take advantage of the systems resources at the similar time. The OS must ensure that the needs of the different users are poised and that each of the programs they are using has enough and separate sources so that a problem with one user doesn't affect the all other users. UNIX, VMS and mainframe OS, like MVS, are examples of multi-user OS.