- Process States :
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- As a process executes, it changes state.
A process may be in one of the following states:
1. New. The process is being created.
2. Running. Instructions are executing.
3. Waiting. The process is waiting for some event to occur (such as an I/O completion (e.g. printf()/ scanf ()) or reception of a signal).
4. Ready. The process is waiting to be assigned to a processor.
5. Terminated. The process has finished execution.
These process states are found all kind of systems.
- Certain operating systems also more finely delineate process states.
- It is important to realize that only one process can be running on any processor core at any instant.
- Many processes may be ready and waiting, however.
- Process Abstraction :
- First obvious component of process is its memory.
- Instructions lie in memory;
- the data that the running program reads and writes sits in memory as well.
- The memory that the process can address (called its address space) is part of the process.
Second important component of the process’s machine state are registers.
Many instructions explicitly read or update registers and thus- clearly they are important to the execution of the process.
Some particularly special registers are also included.
- For example, the program counter (PC) or Instruction Pointer (IP).
- Similarly a stack pointer and associated frame pointer are used to manage the stack for function parameters, local variables, and return addresses.
- Finally, programs often access persistent storage devices too.
- Such I/O information might include a list of the files the process