PROCESS CONCEPTS:
1.The Process:
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is a program in execution.
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It includes program counter,process stack,data section
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program counter-which contains the address of the next instruction to be executed
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process-stack-contains temporary data
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data section-contains global variables.
2. Process State
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The State of a process is defined by the current activity of that process.
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Each Process may be in one of the following states
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New-process is being created
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Running-Instructions are being executed
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Waiting-Process is waiting for some event to occur
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Ready-Process is waiting to be assigned to a processor
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Terminated-process has finished its execution.
Diagram of process state:
3.Process Control Block:
- Each process is represented in the operating system by a process control block.
- Also called as task control block
- it contains pieces of information associated with a specific process
1.process
state-new,running,waiting,halted...
2.program
counter-which contains the address of the next instruction to be
executed
3.CPU
registers-can include accumulators,index register,stack pointer and
general purpose registers,condition code information.
4.CPU scheduling
information-includes process priority,pointers to scheduling queues
and scheduling parameters
5.Memory
Management information-includes about value of base and limit
registers,page tables,segment tables
6.Accounting
Information-includes the amount of CPU and real time used,time
limits,account numbers,process numbers
7.I/O Status
information-includes list of I/O devices allocated to the process,
list of open files
4.Threads
- a process is a program that performs a single thread of execution
- single thread of control allows the process to perform only one task at one time
- modern OS have extended the process concept to allow a process to have multiple threads of execution.
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