Process States
Throughout the lifespan of a process, its execution position may be in one of four states: (linked with each state is generally a queue on which the process resides)
1. Executing: the process is at present running and has control of a CPU
2. Waiting: the process is at present able to run, but must wait until a CPU becomes available
3. Blocked: the process is at present waiting on I/O, either for input to arrive or output to be sent
4. Suspended: the process is at present able to run, but for some reason the OS has not placed the process on the prepared queue
5. Ready: the process is in memory, will execute specified CPU time.
Process Control Block (PCB)
If the OS allows multiprogramming, then it requires keeping track of all the processes. For every process, its process control block PCB is used to track the process''s execution status, together with the following:
1. Its present processor register contents
2. Its processor state (if it is blocked or set)
3. Which resources have been allocated to it
4. Its memory state
5. A pointer to its stack
6. Which resources it needs