A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread Typically system has many processes, some user, some operating system running concurrently on one or more CPUs Concurrency by multiplexing the CPUs among the processes / threads

1. Operating System 17
Process Management
Prof Neeraj Bhargava
Vaibhav Khanna
Department of Computer Science
School of Engineering and Systems Sciences
Maharshi Dayanand Saraswati University Ajmer

2. Multiprogramming and Multitasking
• Multiprogramming needed for efficiency
– Single user cannot keep CPU and I/O devices busy at all
times
– Multiprogramming organizes jobs (code and data) so
CPU always has one to execute
– A subset of total jobs in system is kept in memory
– One job selected and run via job scheduling
– When it has to wait (for I/O for example), OS switches
to another job

3. Multiprogramming and Multitasking
• Timesharing (multitasking) is logical extension in which
CPU switches jobs so frequently that users can interact
with each job while it is running, creating interactive
computing
– Response time should be < 1 second
– Each user has at least one program executing in
memory process
– If several jobs ready to run at the same time  CPU
scheduling
– If processes don’t fit in memory, swapping moves
them in and out to run
– Virtual memory allows execution of processes not
completely in memory

4. Memory Layout for Multiprogrammed System

5. Process Management
• A process is a program in execution. It is a unit of work within the
system. Program is a passive entity, process is an active entity.
• Process needs resources to accomplish its task
– CPU, memory, I/O, files
– Initialization data
• Process termination requires reclaim of any reusable resources
• Single-threaded process has one program counter specifying location
of next instruction to execute
– Process executes instructions sequentially, one at a time, until
completion
• Multi-threaded process has one program counter per thread
• Typically system has many processes, some user, some operating
system running concurrently on one or more CPUs
– Concurrency by multiplexing the CPUs among the processes /
threads

6. Process Management Activities
• Creating and deleting both user and system processes
• Suspending and resuming processes
• Providing mechanisms for process synchronization
• Providing mechanisms for process communication
• Providing mechanisms for deadlock handling
The operating system is responsible for the following
activities in connection with process management:

7. Process Concept
• An operating system executes a variety of programs:
– Batch system – jobs
– Time-shared systems – user programs or tasks
• Textbook uses the terms job and process almost
interchangeably
• Process – a program in execution; process execution must
progress in sequential fashion
• Multiple parts
– The program code, also called text section
– Current activity including program counter, processor
registers
– Stack containing temporary data
• Function parameters, return addresses, local variables
– Data section containing global variables
– Heap containing memory dynamically allocated during run
time

8. Process Concept (Cont.)
• Program is passive entity stored on disk
(executable file), process is active
– Program becomes process when
executable file loaded into memory
• Execution of program started via GUI
mouse clicks, command line entry of its
name, etc
• One program can be several processes
– Consider multiple users executing the
same program

9. Process in Memory

10. Process State
• As a process executes, it changes state
– new: The process is being created
– running: Instructions are being executed
– waiting: The process is waiting for some event
to occur
– ready: The process is waiting to be assigned to
a processor
– terminated: The process has finished execution

11. Diagram of Process State

12. Process Control Block (PCB)
Information associated with each process
(also called task control block)
• Process state – running, waiting, etc
• Program counter – location of
instruction to next execute
• CPU registers – contents of all process-
centric registers
• CPU scheduling information- priorities,
scheduling queue pointers
• Memory-management information –
memory allocated to the process
• Accounting information – CPU used,
clock time elapsed since start, time
limits
• I/O status information – I/O devices
allocated to process, list of open files

13. CPU Switch From Process to Process

14. Threads
• So far, process has a single thread of
execution
• Consider having multiple program
counters per process
– Multiple locations can execute at once
• Multiple threads of control -> threads
• Must then have storage for thread
details, multiple program counters in PCB
• See next chapter

15. Assignment
1. What is process concept? Explain Process Management in
OS
2. Draw and describe the process states