Exam 1

Question 1

PID

Answer 1

Process ID

Question 2

GID

Answer 2

Group ID

Question 3

UID

Answer 3

User ID

Question 4

TSL

Answer 4

Test and Set Lock

Question 5

process

Answer 5

a program in execution

Question 6

daemon

Answer 6

a background process

Question 7

child process

Answer 7

a process created by another process

Question 8

multiprogramming

Answer 8

when multiple processes are running

Question 9

multiprocessing

Answer 9

when multiple CPUs are running processes

Question 10

race condition

Answer 10

two or more processes want to modify a shared resource at the same time and the result depends who runs when

Question 11

quantum

Answer 11

the amount of time before a clock interrupt preempts a process

Question 12

critical section

Answer 12

when the program is accessing the shared data

Question 13

atomic action

Answer 13

a single check, change, and possible sleep action

Question 14

spin lock

Answer 14

a lock that uses busy waiting

Question 15

system call

Answer 15

trapping into the kernel and invoking the operating system

Question 16

throughput

Answer 16

the number of jobs per hour the system completes

Question 17

turnaround time

Answer 17

the averaged time from the moment a job is submitted to the time that it is completed in a batch setup

Question 18

preemptive scheduling

Answer 18

selects a process to run for a set amount of time and after that time if the process is still running it is suspended and another process is allowed to run

Question 19

context switch

Answer 19

switching from one program to another

Question 20

thread

Answer 20

a lightweight process

Question 21

what are the two main functions of an operating system

Answer 21

• an extended machine

- a resource manager

Question 22

What hardware characteristics distinguish between the 4 generation of computers?

Answer 22

vacuum tubes, transistors, ICs, PCs

Question 23

What is the memory hierarchy? Why do computer systems use a memory hierarchy?

Answer 23

registers, cache, main memory, disk drives, tape drives

the higher in the hierarchy the faster the access but the more it costs

Question 24

Why are system calls necessary? What does the fork system call accomplish?

Answer 24

• system calls protect from allowing the user to cause avoidable damage to the system
• creates a child process

Question 25

Which of the following instructions should be allowed only in kernel mode? a) disable all interrupts b) read the time-of-day clock c) set the time-of-day clock d) change the memory map

Answer 25

a, c, d

Question 26

What is a virtual machine?

Answer 26

allows multithreading on a machine that doesn’t support it

Question 27

List some items that might be found in a process table.

Answer 27

Registers, Program counter, Stack Pointer, Priority, GID, UID, PID, PPID, group, time used

Question 28

What are the three process states and four transitions that were discussed in the book? You should be able to reproduce the figure that represents the three process states and four transitions.

Answer 28

• ready, running, blocked

- blocked for input, scheduler picks a process, scheduler picks this process, input becomes available

Question 29

what advantages are there in using threads rather than multiple processes

Answer 29

more can be accomplished at once, faster program speeds, virtualization

Question 30

list two examples of applications that are commonly implemented using threads

Answer 30

• web server

- word processor

Question 31

what are the advantages and disadvantages are there in implementing threads in user space as opposed to kernel space

Answer 31

advantage: more usage of the quantum
disadvantage: less fair to the other processes

Question 32

which is easier: blocking system call or non-blocking system call

Answer 32

blocking system call

Question 33

list four functions defined by the Pthread standard

Answer 33

create, exit, join, yield

Question 34

what four conditions are needed to avoid race conditions

Answer 34

1. no tow processes may be simultaneously inside their critical regions
2. No assumptions may be made about speeds or the number of CPUs
3. No process running outside its critical region may block other processes
4. No process should have to wait forever to enter its critical region

Question 35

what were the problems with the four unsuccessful attempts to implement mutual exclusion functions?

Answer 35

?

Question 36

what two functions are implemented by an operating system that supports semaphores?

Answer 36

up and down

Question 37

what is a binary semaphore

Answer 37

a semaphore that can have only one of two values

Question 38

why don’t we use the monitor system call in every application that needs to implement mutual exclusion

Answer 38

monitor doesn’t work in machines with more than one CPU

Question 39

what mechanism is used to avoid race conditions with multiple CPUs

Answer 39

Message Passing

Question 40

what are six goals that could be used in designing a good scheduling algorithm

Answer 40

• fairness
• policy enforcement
• balance
• throughput
• response time
• meeting deadlines

Question 41

List three scheduling algorithms that could be used for a batch-oriented system

Answer 41

• throughput
• turnaround time
• CPU utilization

Question 42

List three scheduling algorithms that could be used for an interactive-oriented system

Answer 42

response time
proportionality
balance

Question 43

dining philosophers problem

Answer 43

an example of deadlock issue