From man ps:R = Running or RunnableS = interruptable SleepT = sToppedZ = ZombieD = uninterruptible sleep (usually IO)Where does this D come from?
Why is uninterruptible sleep indicated by 'D'?
process;io;history
From the 4BSD ps man page:The state is given by a sequence of  four letters, e.g. ``RWNA''.  The first letter indicates the   runnability of the process: R for runnable processes, T for   stopped processes, P for processes in page wait, D for those   in disk (or other short term) waits, S for those sleeping   for less than about 20 seconds, and I for idle (sleeping   longer than about 20 seconds) processes.