Midterm

Question 1

Name a general trend in going up or down the memory hierarchy?

Answer 1

speed is slower moving down the hierarchy
size is larger moving down the hierarchy
cost is less moving down the hierarchy

Question 2

what is the relationship between the operating system and the kernel?

Answer 2

a kernel is a subset of the operating system

Question 3

do system calls require kernel mode? why?

Answer 3

No, because system calls are like the communication between the operating system and the kernel mode.

Question 4

Describe the relationship between a library procedure and a system-call.

Answer 4

Library procedure initiate a system call to access a memory address

Question 5

Is a program a process?

Answer 5

only when it is running - process is a runnable program

Question 6

How many processes can be run at a time on a single-processor?

Answer 6

1

Question 7

Which of the following does each thread have a separate copy?

Answer 7

address space
global variables
* program counter
* registers
* stack

Question 8

Does an operating system have both user and kernel threads?

Answer 8

No, user will use in the application level and kernel will use operating system

Question 9

Why do operating systems have user or kernel modes of execution?

Answer 9

to protect the operating system

Question 10

What is a microkernel?

Answer 10

a small kernel

Question 11

What is motivating factor behind the design decisions for a microkernel?

Answer 11

bugs

Question 12

What is the UNIX equivalent to the CreateProcess( ) system call?

Answer 12

Fork( )

Question 13

what will be displayed after executing the following code?
fork( );
fork( );
printf(“All done!\n”);

Answer 13

Prints all done four times

Question 14

Name a service that the operating system provides.

Answer 14

Process scheduling
Resource usage
Accessing I/O devices
File system accesses/management

Question 15

What is the stack of a thread?

Answer 15

parameters

local variables

Question 16

The process table contains what kind of information?

Answer 16

process name and state
priority
registers
semaphores

Question 17

What are the major steps of a context switch?

Answer 17

Stopping one process and starting a new one

Question 18

Name 2 or more events that would cause a process to transition to the ready state?

Answer 18

one event is when the process has scheduled an interrupt. Another event is when one process has finished executing and the next process is ready to start executing

Question 19

What does the fork( ) system call do?

Answer 19

Its a process that creates a copy of itself.

Question 20

What does the execve( ) system call do?

Answer 20

Execve( ) is used to overlay a process image that has been created by a call from the fork( ) function.

Question 21

What does pthread_join( ) do?

Answer 21

pthread_join( ) waits for a specific thread to exit

Question 22

Name at least one benefit of using multithreaded programming?

Answer 22

You can run two processes at the same time instead of one at a time but the CPU will think it is only one process.

Question 23

What are the labels for the states that a process may be in?

Answer 23

A. creation
B. termination
C. ready
D. running
E. blocked

Question 24

What are the labels for the transitions between process states?

Answer 24

A. fork or create process
B. Scheduler
C. Exit
D. Scheduler
E. Event handling

Question 25

What process state transitions are not allowed and why?

Answer 25

1. Blocked -> Running (has to go through ready)

2. Ready -> Blocked (can only be blocked if running)

Question 26

Explain the difference between an I/O-bound process and a CPU-process.

Answer 26

The difference between I/O-bound and CPU-bound processes are that the I/O-bound spends more time seeking I/O operations and CPU-bound spends more time performing computational work.

Question 27

Why should a web server not run as a single-threaded process?

Answer 27

A web server that runs as a single-threaded process can only be serviced with one client at a time. This could result in very long wait times for a busy server.

Question 28

What provides an interface to the services provided by an operating system?

Answer 28

System calls

Question 29

Write a code illustrating the typical usage of semaphores to protect a critical region.

Answer 29

#define N 100;
typedef int semaphore;
semaphore mutex = 1;
semaphore empty = N;
semaphore full = 0;

void producer(void) {
int item;

while true {
item = produce_item( );
down(&empty);
down(&mutex);
insert_item(item);
up(&mutex);
up(&full);
}
}