The document provides an overview of processes in operating systems, highlighting their definition as programs in execution and detailing the functionalities of operating systems in process management such as creation, termination, and synchronization. It discusses the process state changes and the role of the process control block (PCB) in storing essential information about each process. Additionally, it introduces the concept of threads as a means for concurrent execution within processes.

1. Amrita
School
of
Engineering,
Bangalore
Ms. Harika Pudugosula
Teaching Assistant
Department of Electronics & Communication Engineering

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 Process Concept
 Process Scheduling
 Operations on Processes
 Interprocess Communication

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 To introduce the notion of a process - a program in execution, which
forms the basis of all computation
 To describe the various features of processes, including scheduling,
creation and termination, and communication
 To explore interprocess communication using shared memory and
message passing
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 Chapter Introduction
 Process Concept
 The Process
 Process State
 Process Control Block (PCB)
 Threads

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Chapter Introduction
• Process - Program in execution
• Need resources to accomplish tasks
• Allocation of resources
• Unit of work in modern time-sharing systems - Process
• OS processes execute system code
• User processes execute user code

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 The operating system is responsible for the following
activities in connection with process management:
• 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
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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
 The Process
 Process - a program in execution
- a process execution must progress in sequential fashion

8.  Multiple parts
• The program code, also called text section - it
includes current activity, as represented by the
value of program counter the contents of
processor’s registers
• Stack containing temporary data
• Function parameters, return addresses, local
variables
• Data section containing global variables
• Heap - memory that is dynamically allocated
during process run time
fig. Process in memory

9.  Program is passive entity stored on secondary storage disk
(executable file)
 Process is active entity, with a PC specifying next instruction to be
execute and a set of associated resources
 Program becomes process when executable file loaded into memory
 Two common techniques for loading executable file
• Double-clicking an icon representing the executable file
• Entering the name of the executable file on command prompt
• Two processes may be associated with the same program, but
separate proces; the text sections are equivalent, the data, heap,
and stack sections vary

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 Process State
As a Process executes, it changes its state (current activity of the
process)
• New - The process is being created
• 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)
• Ready - The process is waiting to be assigned to a processor
• Terminated - The process has finished execution
 Name of the states are arbitary
 Only one process can be running on any processor at any instant,
many processes may be ready and waiting

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fig.

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 Process Control Block
• Contains information associated with each
process - 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 fig. Process Control
Block

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 Process Control Block
• Memory management information – memory
allocated to the process, base and limit
register,page table ,segment table
• 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
 PCB simply serves as the repository for any
information that may vary from process to
process fig. Process Control
Block

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fig.

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 Threads
• Process that performs a single thread of execution
• Consider having multiple program counters per process
• Multiple locations can execute at once
• Modern OS, allows to have multiple threads of execution, more than
one task at a time
• Must then have storage for thread details, multiple program counters
in PCB

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References
1. Silberscatnz and Galvin, “Operating System Concepts,” Ninth Edition,
John Wiley and Sons, 2012.

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Thank you