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Operating Systems
Process Control Management
Prepared by: Dhason
Topic & Structure of the lesson
Process Control Management
• Process
• Process States
• Process Scheduling
Operating Systems
Slide 2 of 25
Learning Outcomes
Process Control Management
• At the end of this lecture YOU should be able to:
- define the term process
- identify process states
- draw and explain process states using process
state diagrams
- describe how process scheduling works
Operating Systems
Slide 3 of 25
Process
Process Control Management
• What is a process?
- it is a program in execution which progresses in a
sequential manner
- it is a unit of work with a unique process
identification
- requires resources like memory, CPU time and
files to complete its task
- resources are allocated when a process is created
or while in execution
Operating Systems
Slide 4 of 25
Process (cont.)
Process Control Management
•
•
the operating system creates and deletes user and
system processes
a process is active while a program is passive
• the operating system keeps track of processes
using a process table
Operating Systems
Slide 5 of 25
Process State Diagram
Process Control Management
new
exit
admitted
terminated
Interrupt / time out
ready
I/O or event
completion
running
scheduler dispatch
I/O or event wait
blocked
Operating Systems
Slide 6 of 25
Process States
Process Control Management
•
as a program executes, it changes states
•
New
- a process has just been created
•
Reasons for process creation
- new batch job
- interactive logon
• a NEW process now becomes READY
• Ready
- the process is waiting to be assigned to a processor
Operating Systems
Slide 7 of 25
Process States (cont.)
Process Control Management
• READY - RUNNING
- instructions are being executed
- a process is using the CPU
- the number of running processes will depend on the
number of processors the computer has
•
A running process now can become BLOCKED, READY
or TERMINATED
• A RUNNING process becomes BLOCKED when :
- the process itself cannot execute because it is waiting
for an I/O operation to complete
- the process is waiting for some external event to happen
Operating Systems
Slide 8 of 25
Process States (cont.)
Process Control Management
•
From BLOCKED the process then becomes READY when:
- an event which the process was waiting for occurs
• A RUNNING process becomes READY when:
- a process has reached its maximum allowable time for
uninterrupted execution
Operating Systems
Slide 9 of 25
Process States (cont.)
Process Control Management
•
From RUNNING the process then TERMINATES when:
- a process has completed
- a process has been aborted
• Reasons for process termination
- normal completion
- invalid instruction
- memory unavailable
• Control is then returned to the operating system
Operating Systems
Slide 10 of 25
Quick Review Questions
Process Control Management
•
For each of the following transitions between process
states indicate whether the transition is possible or not
possible?
ready
ready
blocked
•
running
new
ready
On a system with n number of CPU’s what is the
minimum number of processes that can be in the ready,
running and blocked state?
Operating Systems
Slide 11 of 25
Process Control Block (PCB)
Process Control Management
•
Each process is represented in the operating system as
a process control block (PCB)
• a PCB:
- keeps track of each process
- contains information associated with a specific
process
- serves as a repository of any information that may
vary from process to process
Operating Systems
Slide 12 of 25
Process Control Block Diagram
Process Control Management
Pointer to parent process
Pointer area to child process
Process state
Program counter
Register save area
Memory limits
Priority information
Accounting information
Pointer to files and other
I/O resources
Operating Systems
Slide 13 of 25
Process Control Block
Process Control Management
• Process state – the process states; ready, running,
blocked, terminated
• Program counter – indicates the location for the next
instruction
• Priority information - CPU scheduling information
• Accounting information – statistics on CPU time, job and
process numbers
• I/O status – list of I/O devices which are allocated to
processes
Operating Systems
Slide 14 of 25
Process Scheduling
Process Control Management
• As processes enter the system, they are put on
the job queue
• A new process is put on the ready queue
• The process waits until it is selected for execution
or dispatched and given CPU resources
• Once CPU is allocated the process then runs:
- the process could issue an I/O request and be
placed on a device queue or I/O queue
- the process could create a new sub-process
- the process could be forcibly removed
Operating Systems
Slide 15 of 25
Process Scheduling Diagram
Process Control Management
ready queue
I/O
CPU
I/O queue
I/O request
time slice
expired
child
executes
interrupt
occurs
Operating Systems
fork a child
wait for an
interrupt
Slide 16 of 25
Quick Review Questions
Process Control Management
• What is a process control block?
Operating Systems
Slide 17 of 25
Summary of Main Teaching Points
Process Control Management
• A process is a unit of work in execution which
requires resources.
• The state of a process changes as it executes.
• A process control block represents a process in the
operating system.
• Processes can execute concurrently or
independently from each other.
•
Operating Systems
Slide 18 of 25
Question and Answer Session
Process Control Management
Q&A
Operating Systems
Slide 19 of 25
Next Session
Process Control Management
CPU Scheduling
Operating Systems
Slide 20 of 25