Scheduling

Question 1

Scheduler

Answer 1

A program that manages the processing time different instructions have

Question 2

Pre - emptive

Answer 2

Can respond to a changing circumstance
Can interrupt jobs for other jobs

Question 3

First come first served

Answer 3

Creates queue for jobs in order from first to last
Order of these jobs can not be changed
Good for jobs which require no interactivity
Non- pre-emptive

Question 4

Pros / cons of First come first served

Answer 4

Pros:
- Simple
- No need to estimate job times

Cons:
- No real time response
- Can have high wait time

Question 5

Shortest job first

Answer 5

Estimates job length
Orders jobs from shortest to longest
Non Pre-emptive

Question 6

Pros / Cons of Shortest job first

Answer 6

Pros:
- minimises average wait time

Cons:
- Have to estimate job length
- Larger jobs have higher wait time
- Non pre-emptive
- Not simple

Question 7

Shortest remaining time

Answer 7

Estimates job length
Places jobs in order of shortest remaining time first
A new job can be added and change the order
Pre - emptive

Question 8

Pros / Cons of shortest remaining time

Answer 8

Pros:
- Pre - emptive
- Shortens average wait time

Cons:
- Have to estimate job length
- Long jobs can have higher wait time
- Complex

Question 9

Round robin

Answer 9

Each job is allocated a quantum of processing time
If job is not completed in the quantum it will loop to the back of the queue
This will repeat untill job is completed

Question 10

Pros / Cons of round robin

Answer 10

Pros:
- Pre emptive
- Don’t need to estimate job length
- Fair in allocating processor time
- Has interactivity

Cons:
- Complex
- If a job is not finished in the first quantum , its data will have to be stored in memory , this is inefficient

Question 11

Multi-level feedback

Answer 11

Uses many other algorithms in combination

Question 12

Pros / Cons of Multi-level feedback

Answer 12

Pros:
- Real time response
- Can give priority to a job

Cons:
- Complex
- Expensive
- Lots of memory