Process - A process is an ‘active’ entity as opposed to a
program which is considered to be a ‘passive’ entity. A single program can
create many processes when run multiple times, for example when we open a .exe
or binary file multiple times, many instances begin (many processes are
created).
1)
Process state – Processes may be in one of 5 states, as shown in Figure below –
·
NEW- The process is being created.
·
READY- The process is waiting to be assigned to a processor.
·
RUNNING- Instructions are being executed.
·
WAITING- The process is waiting for some event to occur (such as an I/O
completion or reception of a signal).
·
TERMINATED- The process has finished execution.
3).
PCB (process control block) –
·
Each process is represented in the
operating system by a process control block (PCB).
·
It is also called task control
block.
·
Process State - Running, waiting, etc., as discussed above.
·
Process ID and parent process ID.
·
CPU registers and Program Counter- These need to be saved and restored when
swapping processes in and out of the CPU.
·
CPU-Scheduling information - Such as priority information and pointers to scheduling queues.
·
Memory-Management information- E.g. page tables or segment tables.
·
Accounting information - user and kernel CPU time consumed, account numbers, limits, etc.
·
I/O Status information - Devices allocated, open file tables, etc.
Process control block (PCB)