Flashcards
Scheduling
Cards in this deck (9)
- 1What is a process?A 'process' is a program loaded into memory that can potentially be executed by the CPU. They are also known as 'jobs'.
- 2What are the three states of a process?Its code is running within the CPU
It is waiting for a resource to become available such as a disk file or user input
It is ready to run but is not currently active in the CPU - 3What are the aims of scheduling?Process as many jobs as possible
Make maximum use of CPU time
Be responsive to the user so they are unaware of a delay to their process
Make maximum use of resources such as input-output devices
Be fair to all jobs - none left stranded for too long
Be able to prioritise jobs
Be able to alter priorities according to some rules built into the scheduler
Avoid 'deadlock' - 4how does an operating system schedule programs?maintaining a process control block
- 5Describe First Come, First Serveeach process is queued in order of arrival and then processed till completion.
simplest to implement but very poor in terms of processor efficiency and time lag.
A long process may stop short processes from running and important jobs may also have to wait for less important jobs. - 6Describe Round Robineach process is given a set amount of time and the processor is switched to each process in a circular method. very easy method of implementing scheduling but can be inefficient, as a processor may be allocated to a process that may be waiting for input or output signal so the time is ‘lost’.
- 7Describe Shortest Job Firsthere the job executing time is known or estimated.
When the processor is free the next shortest job is executed.
short jobs being executed very quickly but has the disadvantage of a possibility of the long job experiencing processor starvation. - 8what is processor starvation?where lots of job requests keep coming along which effectively stop the long job being executed.
- 9what is a multi-level queue?When a job arrives it is allocated a priority. This priority is usually dependent on process type, amount of CPU time needed, input/output access or memory size. the job is allocated a queue.
The processor will then process the queues (either using round robin or first come first served) but will complete the higher-priority queue before moving to the next priority queue and so forth.
Information
- Description
- A level Computer Science (Unit 1 - Topic 2) Flashcards on Scheduling, created by Ariana Parr on 21/02/2022.
- Created by
- Ariana Parr
- Views
- 0
- Rating