There are two tasks with specially distinguished process IDs: swapper or sched has process ID 0 and is responsible for paging, and is actually part of the kernel rather than a normal user-mode process. Process ID 1 is usually the init process primarily responsible for starting and shutting down the system. Originally, process ID 1 was not specifically reserved for init by any technical measures: it simply had this ID as a natural consequence of being the first process invoked by the kernel. More recent Unix systems typically have additional kernel components visible as 'processes', in which case PID 1 is actively reserved for the init process to maintain consistency with older systems