Chapter 6 CPU Scheduling Flashcards
What System chooses which process runs next and in what order ?
OS
What is CPU Burst ?
Time a process is using CPU for execution
What is I/O Burst ?
TIme a process is waiting for I/O
What component of OS actually does the scheduling ?
Scheduler
What does the dispathcer do ?
A module that gives CPU control to the process selected by the short term scheduler.
What is the difference between preemptive and non-preemptive scheduling algorithms ?
nonpreemptive = Once process is running, it cannot be interrupted and must be completed by the CPU
preemtptive = can be interrupted when running
How does the CPU scheduler use scheduling algorithms ?
Uses them to queue processes
Name 3 nonpreemtptive scheduling algorithms.
FCFS, SJF, Priority que
Name 3 preemtptive scheduling algorithms.
Round Robin - like FCFS, but w time constraint
SRT - like SJF but preemptive
Preemptive priority
What is starvation ?
lower priority processes may never be chosen from queue
What algs are suceptible to starvation ?
Priority based algs - SJF, SRT, both Priorities algs
What does the short term scheduler do ?
Selects process from ready queue to execute next and allocates CPU
What does the long term scheduler do ?
Selects which processes enter ready queue
What does the medium term scheduler do ?
Performs swaps and performs context switching
What is the difference between asymmetric and symmetric multiprocessing ?
- asymmetric multiprocessing, each processor is assigned a specific task, with (the master) processor controlling worker processors
- In symmetric multiprocessing, each processor runs an identical copy of the operating system and can perform all tasks
