In the mean while the fork() system call the Kernel creates a copy of the parent process's address space and adds it to the child process. But the vfork() system call do not creates any copy of the parent's address space, so it is much faster than the fork() system call. The child process as a answer of the vfork() system call runs exec() system call. The child process from vfork() machine system call runs in the parent's address space  which stop the parent process until the child process exits.