The system program serves as a part of the operating system. It traditionally lies between the user interface and the system calls. The user view of the system is actually defined by system programs and not system calls because that is what they interact with and system programs are closer to the user interface.
Operating system playlist is available at
https://www.youtube.com/playlist?list=PL_obO5Qb5QTE9s7QCNjqk97Q4UUgOseWP
