I know that the system calls are not in the C standard Library. Is there any library (some sort of a system library) where the system calls are?
If there is such a library how is this library linked to the executable program?
System calls are the API between program or library and the kernel. The implementation of system call is in the kernel. C library wraps the system calls which are CPU-architecture specific and supplies a unified C API so the C code could be moved from one architecture to another.