PROCESS
Process is
the term which we always use when we work on a computer application. In our
daily life we use process or program in the same term but it is not correct. “Program
is a set of instruction which always remains in passive mode in the secondary
memory.” Then what is process ? how it is differ from a
program ?
Process
is a program in execution. Imagine that we
have written a program called prog1.c in C. On execution, this program
may read in some data and output some data. But we have to note that when a program
is written and a file is prepared, it is only a passive script i.e, it cannot
cause any input processing or output to happen. Once we compile, and still later
when we run this program, the operations take place. In other view, a program
is a text script with no dynamic behavior. When a program is in execution, the script
is acted upon. It can result some processing and I/O operations. It is for this reason a
process is differentiated from program. While the program is a text script, a
program in execution is a process.
A process passes through
different state throughout its life cycle. There are five states of a process:
1)
New
2)
Ready
3)
Waiting
4)
Running
5)
Terminated
• new:
The process is being created.
• running:
Instructions are being executed.
• waiting:
The process is waiting for some event to occur.
• ready:
The process is waiting to be assigned to a processor.
• terminated:
The process has finished execution
The process passes in a managed
way from one state to another state throughout its life cycle. There are
different data structures at the different state to manage the list of process. In general an OS
may use more than one data structure in the management of processes. It may
maintain a queue for all ready to run processes. It may maintain separate
queues for blocked processes. It may even have a separate queue for each of the
likely events ( according to I/O).
........ to be continued R.P
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