The kernel records a process's creation time and the
CPU time it has consumed including the time spent in user mode and time
spent in system mode.
Processes may also have their own interval timers, which
may be single shot or periodic. These can use signals to notify the process
when timers expire.
Timer objects exist as an Executive support service which
will record the passage of time. After a set time or on expiry of a time
interval the object becomes 'signalled' which will release all waiting