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COMPUTER ENGINEERING 3RD YEAR - BISU > OPERATING SYSTEMS LESSON 3 > Flashcards

OPERATING SYSTEMS LESSON 3 Flashcards

1
Q

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

A

VIRTUAL MEMORY

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2
Q

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

A

VIRTUAL MEMORY

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3
Q

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

A

extremely large, uniform array of storage separating logical memory

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4
Q

This technique frees programmers from concern over memory storage limitations.

A

Virtual Memory

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5
Q

This technique frees programmers from concern over __________________________

A

memory storage limitations.

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6
Q

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

A

DECREASE PERFORMANCE

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7
Q

This is the separation of use logical memory from physical memory

A

Virtual Memory

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8
Q

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

A

smaller physical memory is
available.

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9
Q

Virtual memory is commonly implemented by __________________

A

Demand Paging

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10
Q

Virtual memory can also commonly be implemented by __________________

A

Segmentation System

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11
Q

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

A

Pages

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12
Q

_________________is similar to a paging system but with swapping.

A

Demand-Paging System

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13
Q

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

A

Secondary Memory, Disk

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14
Q

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

A

Swap, Memory

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15
Q

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

A

Process, Pager

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16
Q

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

A

necessary pages

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17
Q

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

A

memory pages , physical memory

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18
Q

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

A

Demand Paging, hardware

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19
Q

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

A

Valid, Not Valid, Valid

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20
Q

Meaning of:
Valid Bit and Not Valid Bit

A

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

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21
Q

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

A

page table entry

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22
Q

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

A

Invalid
The address of the page on disk

23
Q

Access to a page marked invalid causes what?

A

Page Fault

24
Q

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

A

paging hardware, invalid bit is set, trap

25
Q

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 _____________

A

desired page , invalid address error, illegal memory address.

26
Q

Page Replacement takes the following approach

A

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

27
Q

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

A

internal table, valid or invalid memory access

28
Q

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

A

terminate the process, brought in that page

29
Q

(PAGE FAULT HANDLING 3)
FIND WHAT

A

Find a Free Frame

30
Q

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

A

disk operation, newly allocated frame

31
Q

(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 ___________.

A

disk read,
internal table ,
now in memory

32
Q

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

A

instruction
illegal address trap
always been in memory

33
Q

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

A

writing its contents to swap space
page table

34
Q

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

A

the process faulted

35
Q

What is basic to demand paging

A

Page replacement

36
Q

Page replacement completes the separation between the ___________ and ___________.

A

logical memory
physical memory

37
Q

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

A

smaller physical memory

38
Q

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

A

frame allocation algorithm
page replacement algorithm

39
Q

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

A

lowest page fault rate.

40
Q

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

A

particular string of memory string references

computing the number of page faults

41
Q

Beladys’s Anomaly states that

A

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

42
Q

FIFO Algorithm (First In First Out)

A

The simplest page replacement algorithm

43
Q

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

A

FIFO

44
Q

Optimal Algorithm has _______________

A

the lowest page fault rate of all algorithms.

45
Q

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

A

Optimal Algorithm

46
Q

Page replacement schema of Optimal Algorithm

A

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

47
Q

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

A

LRU Algorithm (Least Recently Used)

48
Q

1st One liner definition of LRU

A

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

49
Q

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

A

LRU Algorithm

50
Q

2nd One liner definition of LRU

A

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

51
Q

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

A

OPTIMAL PAGE REPLACEMENT ALGORITHM

52
Q

Bottom note for Lessong 3: As the ________________

A

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

53
Q
A

COMPUTER ENGINEERING 3RD YEAR - BISU (25 decks)

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