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+---
+title: "19-cpu-scheduling"
+aliases: 
+tags: 
+- cosc204
+- lecture
+---
+
+why shedule?
+- keep cpu busy (cpu utilisation)
+- so processed dont hae to spend time waithing for the CPU
+	- even if cpu is always bust executing processses in different orders can change the average time spent in queue
+- cpu burst
+	- ![](https://i.imgur.com/0eTDVVu.png)
+	- (diagram is old the timing will have changed)
+	- between burst - waiting for io
+- so that interactive processes respond quickly
+	- time spent waiting in total
+	- average time between visits to CPU
+	- ![](https://i.imgur.com/w9H7MZ7.png)
+
+criteria
+- CPU utilisation - % time CPU is busy
+- throughput - number of processes completed per time unit
+- turnaround time - (for a single process) length of time from submitted to completed
+- waiting time - (for a single process) time spent waiting for the CPU
+- response time - (for a signle process) average timefrom the submission of a request to a process util the first response in produced
+
+# Scheduling algorithms
+