Operating System

Processes

The Process

Process is a program in execution sometimes its also known as the text section. It also include a process stack for temporary data, data section for global variable and it may also include the heap memory which is allocated at runtime.

stateDiagram
    [*] --> New
    Terminated --> [*]

	New --> Ready
    Running --> Ready
    Ready --> Running
	I/OWaiting --> Ready
	Running --> I/OWaiting
	Running --> Terminated

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Process State

• New : The process is being created.
• Running : Instructions are being executed.
• Waiting : The process is waiting for some event to occur(I / O event).
• Ready : The process is waiting to be assigned to processor.
• Terminated : The process has finished executed.

Process Control Block

Each process is represented in the Operating System by a Process Control Block.

• Process State : The state may be new, ready, running, waiting, halted, and so on.
• Program Counter : The counter indicates the address of the next instruction to be executed.
• CPU Registers : Accumulators, index registers, stack pointers and general purpose registers.

	classDiagram
	      Process : Process State
	      Process : Process Number 
	      Process : Program Counter
	      Process : Registers
		  Process : So on..

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• CPU Scheduling Info. : This information includes the process priority, pointer to scheduling queues.
• Memory-management information : Value of the base and limit registers, the page tables, or the segment tables.
• Accounting information : This information includes the amount of CPU and real time used, time limits, account numbers, jobs or process numbers.
• I/O status information : List of I/O devices allocated to the process.

Thread

Threads are also known as light weight process. Process is a program that perform a single thread of execution.

Process Scheduling

The Objective of the multi-programming is to have some process running at all times, to maximize CPU utilization. The objective of time sharing is to switch the CPU among processes so frequently that users can interact with each program.

Scheduling Queues