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A process moves into the running state when it is chosen for execution. The process's instructions are executed by one of the CPUs (or cores) of the system. There is at most one running process per CPU or core. A process can run in either of the two modes, namely kernel mode or user mode. [1] [2]
The three-state process management model is designed to overcome this problem, by introducing a new state called the BLOCKED state. This state describes any process which is waiting for an I/O event to take place. In this case, an I/O event can mean the use of some device or a signal from another process. The three states in this model are:
The process state is changed back to "waiting" when the process no longer needs to wait (in a blocked state). Once the process finishes execution, or is terminated by the operating system, it is no longer needed. The process is removed instantly or is moved to the "terminated" state. When removed, it just waits to be removed from main memory ...
A process control block (PCB), also sometimes called a process descriptor, is a data structure used by a computer operating system to store all the information about a process. When a process is created (initialized or installed), the operating system creates a corresponding process control block, which specifies and tracks the process state (i ...
This sequence of operations that stores the state of the running process and loads the following running process is called a context switch. The precise meaning of the phrase "context switch" varies. In a multitasking context, it refers to the process of storing the system state for one task, so that task can be paused and another task resumed.
Extract the process control block. Perform a context switch back to the writing process. When the writing process has its time slice expired, the operating system will: [79] Pop from the call stack the registers other than the status register and program counter. Pop from the call stack the status register.
The scheduler is an operating system module that selects the next jobs to be admitted into the system and the next process to run. Operating systems may feature up to three distinct scheduler types: a long-term scheduler (also known as an admission scheduler or high-level scheduler), a mid-term or medium-term scheduler, and a short-term scheduler.
As multitasking greatly improved the throughput of computers, programmers started to implement applications as sets of cooperating processes (e. g., one process gathering input data, one process processing input data, one process writing out results on disk). This, however, required some tools to allow processes to efficiently exchange data.