OPERATING SYSTEMS LESSON 3

Question 1

is a technique that allows the execution of processes that may not be completely
in memory.

Answer 1

VIRTUAL MEMORY

Question 2

The main visible advantage of this scheme is that programs can be larger than physical memory.

Answer 2

VIRTUAL MEMORY

Question 3

Further, Virtual Memory abstracts main memory into mainly __________________ as viewed by the user from physical memory.

Answer 3

extremely large, uniform array of storage separating logical memory

Question 4

This technique frees programmers from concern over memory storage limitations.

Answer 4

Virtual Memory

Question 5

This technique frees programmers from concern over __________________________

Answer 5

memory storage limitations.

Question 6

Virtual memory is not easy to implement,
however and may substantially _____________ if used carelessly

Answer 6

DECREASE PERFORMANCE

Question 7

This is the separation of use logical memory from physical memory

Answer 7

Virtual Memory

Question 8

Virtual Memory separation allows an
extremely large virtual memory to be provided for programmers when only a _________________

Answer 8

smaller physical memory is
available.

Question 9

Virtual memory is commonly implemented by __________________

Answer 9

Demand Paging

Question 10

Virtual memory can also commonly be implemented by __________________

Answer 10

Segmentation System

Question 11

Several systems provide a paged segmentation scheme where segments are broken into _____________________

Answer 11

Pages

Question 12

_________________is similar to a paging system but with swapping.

Answer 12

Demand-Paging System

Question 13

In this virtual memory implementation, processes reside in ________________ ( which is usually a ___________)

Answer 13

Secondary Memory, Disk

Question 14

. When we want to execute a process, we ________it into __________

Answer 14

Swap, Memory

Question 15

When a _____________is to be swapped in, the __________ guesses which page will be used before the process is swapped out again.

Answer 15

Process, Pager

Question 16

Instead of swapping in a whole process, the pager brings only those ________ Into memory.

Answer 16

necessary pages

Question 17

Demand Paging avoids reading into _______________ that will not be used anyway, decreasing the swap time and the amount of _________________ needed.

Answer 17

memory pages , physical memory

Question 18

With __________________, we need some form of _____________ support to distinguish between those pages that are on the disk.

Answer 18

Demand Paging, hardware

Question 19

When this bit is set to “_______”, this value indicates that the page is either __________ or _________ but not currently in disk

Answer 19

Valid, Not Valid, Valid

Question 20

Meaning of:
Valid Bit and Not Valid Bit

Answer 20

a Not in the logical address space of the process.
b currently on the disk.

Question 21

The _________________ for a page that is brought into memory is set
as usual,

Answer 21

page table entry

Question 22

The page-table entry for a page that is not currently in memory is simply marked _____________, or contains the ___________________

Answer 22

Invalid
The address of the page on disk

Question 23

Access to a page marked invalid causes what?

Answer 23

Page Fault

Question 24

The_______________ in translating the address through the page table, will notice that the _______________, causing a ________to the operating system.

Answer 24

paging hardware, invalid bit is set, trap

Question 25

This trap is the result of the operating system’s failure to bring the _____________into memory, rather than an ______________ as a result of an attempt to use an _____________

Answer 25

desired page , invalid address error, illegal memory address.

Question 26

Page Replacement takes the following approach

Answer 26

if no frame is free, we find one that is not currently being used and free it.

Question 27

(PAGE FAULT HANDLING 1) Check an ______________ for this process to determine whether the reference was an __________________.

Answer 27

internal table, valid or invalid memory access

Question 28

(PAGE FAULT HANDLING 2) If the reference was invalid, we _____________. If it is valid, but we have not yet____________, we now page in later.

Answer 28

terminate the process, brought in that page

Question 29

(PAGE FAULT HANDLING 3) FIND WHAT

Answer 29

Find a Free Frame

Question 30

(PAGE FAULT HANDLING 4) Schedule a _____________ to read the desired page into the _______________.

Answer 30

disk operation, newly allocated frame

Question 31

(PAGE FAULT HANDLING 5) When the ___________ is complete, we modify the ____________kept with the process and the page table to indicate that the page is ___________.

Answer 31

disk read, internal table , now in memory

Question 32

(PAGE FAULT HANDLING 6) Start the _______that was interrupted by the___________. The process can now access the page as though it had __________.

Answer 32

instruction illegal address trap always been in memory

Question 33

We can free a frame by _______, and changing the _____________ to indicate that the page is no longer in memory.

Answer 33

writing its contents to swap space page table

Question 34

The freed frame can now be used to hold the page for which ________________________.

Answer 34

the process faulted

Question 35

What is basic to demand paging

Answer 35

Page replacement

Question 36

Page replacement completes the separation between the ___________ and ___________.

Answer 36

logical memory physical memory

Question 37

With this page replacement mechanism, a very large virtual memory can be provided for programmers on a______________.

Answer 37

smaller physical memory

Question 38

To implement demand paging we must develop a _____________ and a ________________.

Answer 38

frame allocation algorithm page replacement algorithm

Question 39

There are many page replacement algorithms but the best is the one with the ________________

Answer 39

lowest page fault rate.

Question 40

An algorithm can be evaluated by running it on a _____________ and ___________________.

Answer 40

particular string of memory string references computing the number of page faults

Question 41

Beladys’s Anomaly states that

Answer 41

“the page fault rate may increase as the number of allocated frames increases”

Question 42

FIFO Algorithm (First In First Out)

Answer 42

The simplest page replacement algorithm

Question 43

When a page must be replaced, the oldest page is chose.

Answer 43

FIFO

Question 44

Optimal Algorithm has _______________

Answer 44

the lowest page fault rate of all algorithms.

Question 45

It simply replaces the page that will not be used for the longest period of time.

Answer 45

Optimal Algorithm

Question 46

Page replacement schema of Optimal Algorithm

Answer 46

algorithms. It simply replaces the page that will not be used for the longest period of time.

Question 47

it associates with each page the time of that page’s last use.

Answer 47

LRU Algorithm (Least Recently Used)

Question 48

1st One liner definition of LRU

Answer 48

it associates with each page the time of that page’s last use.

Question 49

It chooses that page that has not been used for the longest period of time.

Answer 49

LRU Algorithm

Question 50

2nd One liner definition of LRU

Answer 50

It chooses that page that has not been used for the longest period of time.

Question 51

This strategy is the ______________ looking backward in time rather than forward.

Answer 51

OPTIMAL PAGE REPLACEMENT ALGORITHM

Question 52

Bottom note for Lessong 3: As the ________________

Answer 52

As the number of frames increase, the page fault decreases.