To access the services of operating system, the interface is provided by theSystem callsAPILibraryAssembly instructions

The interface to access the services of an operating system is provided by the System calls.

Here's a step-by-step explanation:

1. An operating system provides services to both the users and to the programs.
2. It provides programs an environment to execute. It controls and coordinates the use of the hardware among the various application programs for various users.
3. Applications access these services through system calls.
4. System calls provide the interface between a process and the operating system. These are typically functions that are included in the application programming interface (API) of the operating system.
5. When a program makes a system call, it is making a request to the operating system's kernel.
6. So, to access the services of an operating system, the interface is provided by the System calls.