6 - Processes

Question 1

What is multiprogramming?

Answer 1

OS gives CPU to
another program if current program
must wait on I/O

Question 2

What is Cooperative Multitasking?

Answer 2

Programs can

voluntarily yield CPU to another program

Question 3

What is Preemptive Multitasking?

Answer 3

A program gets a
fraction of a second to execute, then OS
automatically switches to the next program,
and so on
Almost all modern OSes implement this

Question 4

What is Multithreading?

Answer 4

allows even more efficient

multitasking, usually preemptive

Question 5

What is Multitasking?

Answer 5

Concurrent execution of multiple programs
Usually an illusion of parallelism
Can run more processes than there are CPUs

Question 6

What is the use of Multitasking?

Answer 6

Allows us to reduce CPU idling during I/O

Question 7

What is a process?

Answer 7

An abstraction of a program in execution.

Question 8

Is a program the same thing as a process?

Answer 8

NO!
Program is PASSIVE
Process is active

Question 9

Does a process get its own address space? What is in this address space?

Answer 9

• text section: the program code
• data section: global variables, constant
variables
• heap: memory for dynamic allocation during run time
• stack: temporary data (parameters, return address, local variables)

Question 10

What is the Process Control Block (PCB)?

Answer 10

A data structure comprising of bits of information needed by the OS for process management.

Question 11

What are the typical parts of the PCB?

Answer 11

HIGH LEVEL
- Process/Memory/File Management

• process state
• program counter, CPU registers
• priority, pointers to various queues
• memory management info: eg. page tables, segment
tables, etc.
• accounting info: eg. CPU time, timeout values, process
numbers, etc.
• I/O status info: open files, I/O devices, etc.

Question 12

What is a Process Table?

Answer 12

A collection of all PCBs

Question 13

Which system call does UNIX define to create a new process?

Answer 13

fork()

Question 14

What is a Parent Process?

Answer 14

The process that is creating a new process

Question 15

What is a Child Process?

Answer 15

A newly created process

Question 16

What is a PID?

Answer 16

A unique process identifier - Each process gets one

Question 17

Which system call does UNIX define to terminate a process?

Answer 17

exit() or kill()

Question 18

How do you start an external program in UNIX?

Answer 18

First fork() to create a new process, then start external program with exec()

Question 19

What does a PID of 0 mean?

Answer 19

The process is the child process.

Question 20

What does a PID < 0 mean?

Answer 20

An error occurred.

Question 21

What is the difference between the system() and popen() C functions?

Answer 21

system() just uses fork() to create a child process that executes the command

popen() opens a pipe between the parent and child (The parent has control over the child’s input and output streams).

Question 22

What is the difference the UNIX and Windows process organization?

Answer 22

UNIX - Parent and child processes continue to be associated, forming a process hierarchy

Windows - All processes are equal, the parent process can give the control of its children to any other process.

Question 23

What is the init or systemd process?

Answer 23

The first process started after booting?

Question 24

What is the PID of init?

Answer 24

Always 1

Question 25

What is an orphaned process? Which process adopts orphaned processes?

Answer 25

Parent terminates before child init

Question 26

``` Which of the following executes in kernel mode? • A user program • A library function call • A system call • A system call wrapper function ```

Answer 26

A system call

Question 27

In C, printf() is a system call. • True • False

Answer 27

False

Question 28

When 4 programs are executing on a computer with a single CPU, how many program counters are there?

Answer 28

4 - One for each process

Question 29

When does a program become a process?

Answer 29

When it is executed

Question 30

What is the name of the PCB data structure in Linux?

Answer 30

Process Control Block

Question 31

What is CPU utilization?

Answer 31

Probability that at least one of the processes is not waiting on I/O

Question 32

What is the function to create a new process in Windows?

Answer 32

CreateProcess()

Question 33

Why would a process want to create a new process?

Answer 33

• System initialization (boot) - background processes - daemons, services • Application decides to spawn additional processes - eg. to execute external programs or to do parallel work • A user requests to create a new process - eg. launching an application from desktop • Starting a batch job - mainframes

Question 34

What us a daemon?

Answer 34

A computer program that runs as a background process, rather than being under the direct control of an interactive user.

Question 35

Does each process have its own address space?

Answer 35

YES

Question 36

What are the different methods for allocating resources for a new process?

Answer 36

Directly from OS A subset of parents resources Parent shares resources Hybrids

Question 37

What options does a parent have after they spawn a new child process?

Answer 37

Wait until the child is finished Continue to operate concurrently Operate concurrently and synchronize with child