Most devices are slow compared to CPU operations. Maximize resource use – favor processes that will use underutilized resources.Keep scheduling time and context switch time at a minimum. Minimize overhead – don’t waste too many resources.Be predictable – a given job should take about the same amount of time to run when run multiple times.
#Timeslice photoshop windows#
Microsoft Windows 3.1 or Apple MacOS prior to OS X Then it is a cooperative, or non-preemptive If a scheduler cannot take the CPU away from a process The last two events in the above list may cause Of a running state to let another process run. The ability to get invoked by an interrupt and move a process out The scheduler may then decide to preempt the currently-running process and move this newly- ready process into the running state.Ī scheduler is a preemptive scheduler if it has The current process goes from the running to the waiting state because it issues an I/O request or some operating system request that cannot be satisfied immediately.Ī timer interrupt causes the scheduler to run and decide that a process has run for its allotted interval of time and it is time to move it from the running to the ready state.Īn I/O operation is complete for a process that requested it and the process now moves from the waiting to the ready state. There are four events that may occur where the scheduler needs to Whether the currently running process should continue running and, if not, Operating system that is responsible for deciding The process scheduler is the component of the Ready state and gets placed on the run queue. Is complete, the process moves from the waiting state to the Pointers to a process control block, which stores all information and state about a process. That are ready to run and not blocked on input/output or anotherīlocking system request, such as a semaphore. Operating system keeps a list of all processes To provide good time-sharing performance, we may preempt a running process Most systems have a large number of processes with short CPU bursts interspersedīetween I/O requests and a small number of processes with long CPU bursts. Quickly enough to give the illusion that many processes are running at the same time. Realizing that you could preempt a process and let To run another process when a process has to wait on an I/O operation.
We could keep several programs in memory and switch the processor
In increasing overall system throughput was the realization that In the half second it might take you to hit the next key as you’re typing. Take you to skim a web page before you click on a link - or 1.2 billion instructions It can run 24 billion instructions in the ten seconds it might Instructions per second (and this does not even count multi-core Waking up periodically to check some state.Ĭonsider a 2.4 GHz processor. Since most of these programs are waiting for user input, a network message, or sleeping and The time, all these processes collectively are using less than 3% of the CPU. Spreadsheet, several shell windows, Photoshop, iTunes, and various This includes a few browser windows, a word processor, As I write this on my Mac, I have 44 processes running Most interactive processes, in fact, spend the vast bulk of their existenceĭoing nothing but waiting on data. Even though it readsĪnd writes data, it spends most of its time processing that data. A video transcoder isĪn example of a process with long CPU bursts. Interactive burstsĬompute-intensive processes, conversely, spend more time running instructions and Interactive processes spend more time waiting for I/O andĮxample of an interactive process with short CPU bursts. The period of computation between I/O requests is called the CPU burst. After that, it executes more instructions and then, again, (computing) and then makes some I/O request, for example, to read or write data to a file or to If you look at any process, you’ll notice that it spends some time executing instructions The finest eloquence is that which gets things done the worst is that which delays them.
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