The two kinds of processes that vie for a place in the system resources queue are user processes and phantom processes. The user process is associated with a serial port or a networked device and is expected to require some kind of input/output through that port. An example is a simple data entry program run on a dumb terminal.
The phantom process usually is not associated with a serial port and is not expected to require any kind of input/output through that port. A typical example of such a process is the Spooler, which handles print jobs. Another example is the Scheduler, which determines when jobs get processed.
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