Modern computers are mainly divided into two parts based on the field of application. For example, a general practical computer, a special practical computer, a common practical computer stores different types of programs. New programs can be saved on this computer and old programs can be changed or deleted. In this case, the user gets the benefit of using a special part of the computer useful for work or adding or modifying any particular part. Special practical computers, on the other hand, are only designed for a specific purpose. A specific program is permanently stored on this computer. Even the scope of application of special practical computers is limited. For example , special practical computers used to guide submarines in the ocean.