A process goes through a series of
discrete process states. The five general categories of process states are:
·
New
·
Ready
·
Running
·
Blocked
·
Terminated
Some authors are describes a process has four states
(by eliminating New state).
The above five states are briefly explained below.
 |
| Process States |
New
The process is being created. But not yet been
admitted to the pool of executable processes by the operating system. Although
its process control block has been created.
Ready
A ready process possesses all the resources needed
for execution excepts the processor. The
process is waiting to be assigned to a processor.
Running
The process
that is currently being executed. On a single processor system, at most one
process may be at running time at any point of time. The running process
executes its sequence of instructions and may call on the operating system to
perform services such as an I/O operation or synchronization via signal
exchange.
Blocked/Waiting/Suspended
A process that cannot execute until some
event occurs, such as the completion of an I/O operation, a synchronization
signal etc. such processes are normally excluded from competition for executing
until the suspending condition is removed.
Terminated
The process has finished
execution.
At any time, a number of active processes occupy
different states. The collective state of all processes and resources (busy, free)
in the system is known as global system
state.
In a system with single CPU, only one
process may be running at any time but several processes may be ready and
several processes may be blocked. Operating system keeps a ready list of ready
processes and a blocked list of blocked processes.
NEXT: Scheduling
Previous: Process management
Index : Operating System
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