Quiz #4

Question 1

How many program can execute at a time without a O/S?

Answer 1

Without an O/S, only one program can be executed at a time

Question 2

How do you change the running program

Answer 2

A CPU reset and some way of loading a new program (flashing, loading from tape, etc.) is required to change the running program,.

Question 3

How much control does the running program have?

Answer 3

The running program has full control and 100% use of the resources of the computer(since It is the only thing running)

Question 4

How many programs can be ran with a O/S?

Answer 4

O/Ses allow more than one program to be loaded at a time and allow us the ability to switch between loaded programs using the concept of a process

Question 5

What is a process? What can you do with them

Answer 5

a process is a program in execution. A process can be paused, restarted, stored and executed

Question 6

What are the parts of a process?

Answer 6

• Processor registers including the program counter
• The program code, also called text section
• Stack containing temporary data; Function parameters, return addresses, local
  variables
• Data section containing global variables
• Heap containing memory dynamically
  allocated during run time

Question 7

What is a process’s address space? What are segments?

Answer 7

• A process’s address space is the range of memory addresses accessible by that process.

The address space is comprised of 3
segments and the heap. The text
segment, contains the executable code
(called the program text, but it is NOT
text!). the data segment contains
constant and global data. The stack
segment contains local variables.
Highest Memory Address

Stack
Heap
Data
Text

Question 8

A program is a ____ entity stored on disk ( ____ ___), a process is ___

Programs become ___ when executed

every process must have ____ ____ ____

Several process may have the ___ ___

Answer 8

passive, executable file, active

process

exactly one program

same program

Question 9

What is a process

Answer 9

A process is an activity of some kind. It
has a program, an address space input, output
and a register state.

Question 10

What is a program?

Answer 10

A program is a set of executable instructions
that may be stored on disk, not necessarily
doing anything

Question 11

If a program is running ___, it counts as ___ processes. The fact that ___ processes are running the same program doesn’t matter. They are ___ ____ processes.

Answer 11

twice, 2, two, 2 distinct

Question 12

Which is a program and a process? A movie on a dvd, playing the movie

Answer 12

program - a movie on a dvd
process - playing the movie

Question 13

Two users are logged into a single-CPU Linux server. User #1 begins a lengthy process to calculate pi to 50 decimal places: 3.14159265358979323846…. User #2 begins a equally lengthy process to sort 1000 names. Both users claim that the CPU is working on her problem. How can this be? There is only 1 CPU.

Answer 13

O/Ses allow more than one program to be loaded at a time and allow us the ability to switch between loaded programs using the concept of a process.

Question 14

• CPU switches from process to process quickly, giving the illusion of ____
• Each process is allowed to run for tens or hundreds of millisecond stretches (called a ____ ____ or ____ )
• This rapid switching is called _____

Answer 14

parallelism

time slice, quantum

multiprogramming

Question 15

How does the CPU do multiprogramming?

Answer 15

• multiprogramming through rapid
  context switching between processes amounts to the O/S abstracting a single physical CPU into multiple virtual CPUs (one per process).
• From each process’s point of view, it is running
  on a dedicated CPU.

Question 16

What is the core component of the operating system kernel? What is above that layer?

Answer 16

process scheduler

the set of processes to be sequentially executed

Question 17

As process executes, it changes state. What are those states and what do they mean?

Answer 17

• new: The process is being created
• running: Instructions are being executed
• waiting: The process is waiting (blocked) for some event to occur
• ready: The process is waiting to be assigned to a processor
• terminated: The process has finished
  execution

Question 18

What is the diagram of process state?

Answer 18

1. Process newly created blocks for input, New -> Ready
2. Process picked to run becomes available, Ready -> Running
   3 - Another process picked to run, Running -> Ready
   4 - Process, Running -> Waiting
   5 - Input, Waiting > Ready
   6 - The process ends, Terminated

Question 19

What is the process control block(PCB)

Answer 19

an array of structures maintained by the kernel

Question 20

What do PCB entires contain?

Answer 20

information about the process’ state, including its program counter, stack pointer, memory allocation, the status of its open files, its accounting and scheduling information, etc

Everything that must be know to transition a process between running, ready and blocked states

Question 21

What is the task control block?

Answer 21

Information associated with each process
(also called task control block)

Question 22

What is PCB components and what do they mean?

Answer 22

• Process state – running, waiting, etc
• Program counter – location of instruction to next execute
• CPU registers – contents of all process-
  centric registers
• CPU scheduling information- priorities,
  scheduling queue pointers
• Memory-management information –
  memory allocated to the process
• Accounting information – CPU used,
  clock time elapsed since start, time limits
• I/O status information – I/O devices
  allocated to process, list of open files

Question 23

Which of the following would NOT likely be stored in a PCB entry?
❑ Current Time
❑ Process’s State
❑ # of Running processes
❑ Stack Pointer
❑ Scheduler’s State

Answer 23

❑ Current Time

Question 24

List at least 3 elements that every process must have.

[Hint: what must be stored in order to completely halt then fully restore a running process?]

Answer 24

Process Identifier, Program Counter (PC), Process State

Question 25

What is the point of multiprogramming?

Answer 25

Multiprogramming aims to have a process running at all times to maximize CPU utilization

Question 26

Where does the process scheduler selects a ‘Ready’ process? Where do other ‘ready’ process wait? Where are 3 things a process will either be?

Answer 26

• The process scheduler selects a ‘Ready’ process for execution on the CPU
• All other ‘Ready’ processes wait in a Ready Queue
• Processes are either running, in the Ready Queue or waiting on I/O in an I/O Queue.

Question 27

What is a short-term scheduler or Cpu scheduler?What is a Long-term scheduler (or job scheduler)?

Answer 27

Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU
* Sometimes the only scheduler in a system
* Short-term scheduler is invoked frequently (milliseconds) ⇒ (must be fast)

Long-term scheduler (or job scheduler)
– selects which processes should be brought into the ready queue
* Long-term scheduler is invoked infrequently (seconds, minutes) ⇒ (may be slow)
* The long-term scheduler controls the degree of multiprogramming

Question 28

What can process either be describer as?

Answer 28

• I/O-bound process – spends more time
  doing I/O than computations, many short
  CPU bursts
• CPU-bound process – spends more
  time doing computations; few very long
  CPU bursts

Question 29

Describe CPU utilization with 20% I/0 wait, 50% IO wait, and 80% I/o wait

Answer 29

20% reaches higher cpu utilization faster
50 has is in-between 20% and 80% I/o wait(bingo closer to 20%), and *0% as a steady sloper

Question 30

What is a I/O-bound process? What is CPU - bound process?

Answer 30

• A process that spends most of its time waiting on I/O is said to be an I/O-bound process.
• A process that spends most of its time running of the CPU is said to be a CPU-bound process.

Question 31

What is the context or state of a process? Where is it stored? What does it include?

Answer 31

• The context or state of a process is all the information needed to suspend and later restore a running process
• The context is the information stored in the PCB and includes
• CPU registers & program counter
• memory management information
• process state

Question 32

• Switching the CPU from a running process to another ready process amounts to
• performing a _____ ____ on the current
  process.
• performing a ____ ____ on the process to
  resume.

Answer 32

state save

state restore

Question 33

What is context switching?

Answer 33

• Switching from one process to another is known as a context switch.

Question 34

Is context switching costly? What does the time depend on? What is it dependent on?

Answer 34

• Context switching is costly, typically requiring a few milliseconds of time during which no useful work is being done.
• Context switch time depends on the number of CPU registers that must be saved/restored.
• Context switch time highly dependent on hardware support. Some CPUs can load/store all registers with a single instruction.

Question 35

• The creating process is called the ____ _____
• The created process is called the _____ ____
• All processes are identified by a ____ _____

Answer 35

parent process
child process
Process ID (PID) number

Question 36

In Unix, we use the ____ system call to create a new process
* In Windows, use the ________ Win32
API to create a new process
* What typically one of two things happens after a new process is created
1.
2.

Answer 36

fork( )
CreateProcess( )

1. The parent continues to execute concurrently with its child (or children)
2. The parent waits until its child (or children) has terminated before continuing

Question 37

How does fork() work? How is it implemented?

Answer 37

• fork() creates an exact clone of the calling process. The parent and child processes have the same memory image (program). The child’s initial address space (program + variables) is a copy of the parent’s.
• Usually, the child process executes an execv() system call to change its memory image and run a new program
• Some Unix implementations share the process image (program text) between parent and all its children. The child process may subsequently change its process image with a call to execv()

Unlike the Unix implementation, CreateProcess() combines the steps of forking and process image replacement. Thus, the parent and child’s
address spaces are distinct from the start.

Question 38

What are the key differences between a
program and a process?

Answer 38

Program: Passive. It remains inactive until executed. The program instructions are stored on a secondary storage device like a hard drive.
Process: Active. It’s a dynamic entity that comes alive when the program is loaded into memory and starts executing. A process can be in various states like running, waiting, or terminated.

Question 39

What are the typical conditions which terminate a process?

Answer 39

Typical conditions which terminate a process:
1. Normal exit (voluntary).
2. Error exit (voluntary).
3. Fatal error (involuntary).
4. Killed by another process (involuntary)

Unix → exit()
Windows → ExitProcess

Question 40

What is waitpid()

Answer 40

• A parent can wait for its child process to exit by using the waitpid() system call
  pid_t waitpid(pid_t pid, int *child_status, int options);
  where,
• pid is the process ID of the child we are waiting to complete.
• child_status is an integer returned by the terminated child process.
• options can be set to 0.

Question 41

Typically, after executing a ____ function , the newly created child process will change its program.
* The ____ function can be used to do this.

Answer 41

fork()
execv()

Question 42

Is fork a system call?

Answer 42

yes

Question 43

What does the fork function return when it fails?

Answer 43

-1

Question 44

All children of the parent process have the same process id?

Answer 44

False

Question 45

How do you create a new process

Answer 45

unix fork

Question 46

Every time you spawn a child process it inherits the parents stack from the parents

Answer 46

true