The call stack stores information about the active subroutines of a computer program. Before jumping to a new subroutine, the caller pushes the return address and the CPU registers values of the calling subroutine onto the stack and the CPU registers are available for the called subroutine to use.

When the called subroutine finshes, it pops the return address and cpu registers of the calling subroutine and execution of the calling subroutines resumes.