Please check the answers for Q4 & Q5
4)The two categories of services and functions provided by an operating system are: User services and system services

User services provides functions that are helpful to users, including user interface, program execution, I/O operations, file system operations, communication, and error detection

System services are not meant to help users but to ensure that the system itself runs efficiently.  Systems with multiple users can gain efficiency by sharing the computer resources among the users. System services include resource allocation, accounting, protection and security.

5) Three general methods of passing parameters are

a. Pass parameters in registers

b. Registers pass starting addresses of blocks of parameters

c. Parameters can be placed, or pushed, onto the stack by the program, and popped off the stack by the operating system