Two categories are:-
1. One set of operating system services provides functions that are helpful to the user. These services include the user interface, program execution, I/O operations, file-system manipulation, communications, and error detection.
2. Another set of operating-system functions exists not for helping the user, but rather for ensuring the efficient operation of the system itself. Systems with multiple users can gain efficiency by sharing the computer resources among the users. This set of services includes resource allocation, accounting, and protection and security.
( fodDalo team )