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Memory and Process
Management, Major resource types, life cycle of a…
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life cycle of a process
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Running
A process in the running state has all of the resources that it needs for further execution, including a processor
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-A process is executed until it must wait,typically for the completion of some I/O request.
-Scheduling of this kind is a fundamental operating-system function.Almost all computer resources are scheduled before use and CPU is one of the primary computer resources.
-The success of CPU scheduling depends on an observed property of processes : process execution consists of a cycle of CPU execution and I/O wait.
-Process execution begins with a CPU burst. That is followed by an I/O burst,which followed by another CPU burst,then another I/O burst, and so on.
-The durations of CPU bursts may vary greatly from process to process and from computer to computer(exponential or hyper-exponential)
-An I/O-bound program typically has many short CPU bursts.A CPU-bound program might have a few long CPU bursts.
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-Whenever the CPU becomes idle,the operating system must select one of the processes in the ready queue to be executed.The selection process is carried out by the short-term scheduler (or CPU scheduler).
-Note that the ready queue is not necessarily a first-in, first-out (FIFO) queue.
-As we shall see when we consider the various scheduling algorithms,a ready queue can be implemented as a FIFO queue,a priority queue,a tree, or simply an unordered linked list.
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The operating system will ignore the interrupts from some sources so that a particular job can be finished as quickly as possible.
-These are some interrupts (such as those from error conditions or problems with memory) that are so important that they can`t be ignored.These non-maskable interrupts (NMIs) must be dealt with immediately
-An event that change the sequence in which a processor execute instructions.Prevent a process from monopolizing the system.
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- MUTUAL EXCLUSION
2.HOLD AND WAIT
- NO PREEMPTION
- CIRCULAR WAIT