Homework 2

Sarah Diesburg

Operating Systems

COP 4610

Why does OS loader set kernel mode? OS needs to run with full privileges

Sets more restrictive user mode bit for user programs

Protects OS from errant user programs

Three Processes

Process A

Process B

Process C

Time

0 100 200 300 400 500 600 700 800

First In, First Out

Process A

Process B

Process C

FIFOTime

0 100 200 300 400 500 600 700 800

BC A

First In, First Out

Process A

Process B

Process C

FIFO

Average response time

= [(300-50) + (500-150) + 0]/3 = 200

Time

0 100 200 300 400 500 600 700 800

BC A

First In, First Out

Process A

Process B

Process C

FIFO

Average wait time

= [(300-50) + (500-150) + 0]/3 = 200

Time

0 100 200 300 400 500 600 700 800

BC A

First In, First Out

Process A

Process B

Process C

FIFO

Average turnaround time

= [(500-50) + (900-150) + (300-0)]/3 = 500

Time

0 100 200 300 400 500 600 700 800

BA BC A

Round Robin (Time slice = 100)

Process A

Process B

Process C

RRTime

0 100 200 300 400 500 600 700 800

C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C B

Process A

Process B

Process C

RR

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C B

Process A

Process B

Process C

RR

Average response time

= [(100-50) + (300 – 150) + 0]/3 = 66.7

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C B

Process A

Process B

Process C

RR

Average wait time

= {[(100–50) + (400–200)] + [(300–150) + (600–400)]

+ [0 + (200–100) + (500–300)]}/3 = [250 + 350 + 300]/3 = 300

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C B

Process A

Process B

Process CRR

Average turnaround time= [(500 – 50) + (900 – 150) + (600 – 0)]/3 = 600

Round Robin (Time slice = 100)

Time

0 100 200 300 400 500 600 700 800

C A C B A C B

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C A

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C A

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C A

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C A B

Shortest Job Next

Process A

Process B

Process C

SJNTime

0 100 200 300 400 500 600 700 800

C A B

Shortest Job Next

Process A

Process B

Process C

SJN

Average response time

= [(300-50) + (500-150) + 0]/3 = 200

Time

0 100 200 300 400 500 600 700 800

C A B

Shortest Job Next

Process A

Process B

Process C

SJN

Average wait time

= [(300-50) + (500-150) + 0]/3 = 200

Time

0 100 200 300 400 500 600 700 800

C A B

Shortest Job Next

Process A

Process B

Process C

SJN

Average turnaround time

= [(500-50) + (900-150) + (300-0)]/3 = 500

Time

0 100 200 300 400 500 600 700 800

C A B

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A C

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A C

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A C B

Shortest Remaining Time First

Process A

Process B

Process C

SRTFTime

0 100 200 300 400 500 600 700 800

C A C B

Shortest Remaining Time First

Process A

Process B

Process C

SRTF

Average response time

= [0 + (500-150) + 0]/3 = 117

Time

0 100 200 300 400 500 600 700 800

C A C B

Shortest Remaining Time First

Process A

Process B

Process C

SRTF

Average wait time

= [0 + (500 – 150) + (250 – 50)]/3 = 183

Time

0 100 200 300 400 500 600 700 800

C A C B

Shortest Remaining Time First

Process A

Process B

Process CSRTF

Average turnaround time= [(250 – 50) + (900 – 150) + (500 – 0)]/3 = 483

Time

0 100 200 300 400 500 600 700 800

C A C B