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In many cases programs may appear to be hung, but are making slow progress, and waiting a few minutes will allow the task to complete. Modern operating systems provide a mechanism for terminating hung processes, for instance, with the Unix kill command, or through a graphical means such as the Task Manager's "end task" button in Windows (select the particular process in the list and press "end ...
Many operating systems, for example Windows, [1] Linux, [2] and macOS [3] will run an idle task, which is a special task loaded by the OS scheduler on a CPU when there is nothing for the CPU to do. The idle task can be hard-coded into the scheduler, or it can be implemented as a separate task with the lowest possible priority.
For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the "System Idle Process". On x86 processors, the opcode of HLT is 0xF4.
In either of these cases, the process moves to the "terminated" state. The underlying program is no longer executing, but the process remains in the process table as a zombie process until its parent process calls the wait system call to read its exit status , at which point the process is removed from the process table, finally ending the ...
However, the idle process does not use up computer resources (even when stated to be running at a high percent). Its CPU time "usage" is a measure of how much CPU time is not being used by other threads. In Windows 2000 and later the threads in the System Idle Process are also used to implement CPU power saving.
At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called "I/O bound"), and those that are fully utilizing the CPU ("CPU bound"). In early systems, processes would often "poll" or "busy-wait" while waiting for requested input (such as disk, keyboard or network input). During this time ...
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In computer operating systems, a process (or task) may wait for another process to complete its execution. In most systems, a parent process can create an independently executing child process . The parent process may then issue a wait system call , which suspends the execution of the parent process while the child executes.