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    <p><strong>Process:</strong></p> <ul> <li>An executing instance of a program is called a process.</li> <li>Some operating systems use the term ‘task‘ to refer to a program that is being executed.</li> <li>A process is always stored in the main memory also termed as the primary memory or random access memory.</li> <li>Therefore, a process is termed as an active entity. It disappears if the machine is rebooted.</li> <li>Several process may be associated with a same program.</li> <li>On a multiprocessor system, multiple processes can be executed in parallel.</li> <li>On a uni-processor system, though true parallelism is not achieved, a process scheduling algorithm is applied and the processor is scheduled to execute each process one at a time yielding an illusion of concurrency.</li> <li><strong>Example:</strong> Executing multiple instances of the ‘Calculator’ program. Each of the instances are termed as a process.</li> </ul> <p><strong>Thread:</strong></p> <ul> <li>A thread is a subset of the process.</li> <li>It is termed as a ‘lightweight process’, since it is similar to a real process but executes within the context of a process and shares the same resources allotted to the process by the kernel.</li> <li>Usually, a process has only one thread of control – one set of machine instructions executing at a time.</li> <li>A process may also be made up of multiple threads of execution that execute instructions concurrently.</li> <li>Multiple threads of control can exploit the true parallelism possible on multiprocessor systems.</li> <li>On a uni-processor system, a thread scheduling algorithm is applied and the processor is scheduled to run each thread one at a time.</li> <li>All the threads running within a process share the same address space, file descriptors, stack and other process related attributes.</li> <li>Since the threads of a process share the same memory, synchronizing the access to the shared data within the process gains unprecedented importance.</li> </ul> <p>I borrowed the above info from the <a href="http://web.archive.org/web/20100807021758/http://kquest.co.cc/2010/03/program-process-task-thread" rel="noreferrer"><strong>Knowledge Quest! blog</strong></a>.</p>
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    1. POWhat is the difference between a process and a thread?
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    1. USGanesh Kamath - 'Code Frenzy'
    1. USKumar
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    1. COKumar: From my knowledge, threads do not share the same stack. Otherwise it wouldn't be possible to run different code on each of them.
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      1. USMihai Neacsu
    2. COYup I think @MihaiNeacsu is right. Threads share "code, data and files" and have their own "registers and stack". Slide from my OS course: http://i.imgur.com/Iq1Qprv.png
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      1. USShehaaz
 

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