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OS > Module 5 > Flashcards

Module 5 Flashcards

1
Q

A system that has several disk platters made of metal or glass with a flat circular shape.

A

Magnetic Disk System

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2
Q

Where is the information stored in a magnetic disk?

A

In a magnetic recording material covering the two surfaces.

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3
Q

The disk surface is divided into ________ then subdivided into ________.

A

divided into TRACKS then subdivided into SECTORS

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4
Q

True or False
In a Disk Structure, the head doesn’t touch the disk surface but it floats microns above supported by a cushion of air.

A

True

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5
Q

What is the typical rotation speed of hard disks?

A

4500 to 7500 rpm.

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6
Q

True or False
In a hard disk, the faster the disk rotation, the higher the transfer rate.

A

True

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7
Q

True or False
If a hard disk rotates faster, it also becomes louder and hotter.

A

True

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8
Q

True or False
Modern hard disks read all sectors of a track in one turn (Interleave 1:1)

A

True

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9
Q

In modern hard disks, the rotation speed is _______.

A

Constant

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10
Q

It is when the head contacts the disk surface, scraping the recording medium off the disk, destroying data.

A

Head crashes

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11
Q

It is one of the earliest secondary-storage media.

A

Magnetic Tape

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12
Q

It was too slow compared with the access time of main memory and slower than disks.

A

Magnetic Tape

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13
Q

It is currently used mainly for backup, rarely useful information, and for transferring information.

A

Magnetic Tape

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14
Q

It provides the bulk of secondary storage for modern computers.

A

Magnetic Disks

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15
Q

In a magnetic disk, information is recorded ______________ on the sector under the read-write head.

A

Magnetically

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16
Q

A __________ system has a separate read-write head for each track.

A

Fixed-head system

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17
Q

This system allows the computer to switch from track to track quickly/

A

Fixed-head system

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18
Q

This system requires a large number of heads, making it expensive.

A

Fixed-head system

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19
Q

A _______________ system has only one read-write head per surface and the system moves the head to access a particular track (slower but less expensive).

A

Moveable-head system

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20
Q

All the tracks on one drive that can be accessed without moving the heads are called a _______.

A

Cylinder

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21
Q

____________ are coated with a hard surface, so the read-write head scans it directly on the disk surface without destroying the data.

A

Floppy Disks

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22
Q

One of the most commonly used floppy diskettes capable of storing 1.44 MB of data.

A

3.5” floppy diskette

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23
Q

How much data can a 3.5” floppy diskette store?

A

1.44 MB

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24
Q

A disk normally has a _________ indicating which files are on the disk.

A

Device directory

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25
Q

The directory lists the file by ________, and includes necessary information.

A

Name

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26
Q

The system stores the disk directory on the device, often at some ________.

A

Fixed disk address

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27
Q

Modern disks are addressed as ______________________ of logical blocks, the smallest unit of transfer, typically 512 bytes.

A

Large one-dimensional arrays

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28
Q

In modern disks, what is the smallest unit of transfer?

A

512 bytes

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29
Q

Some disks can be _________________ to choose another size such as 1024 bytes.

A

Low-level formatted

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30
Q

What are the two ways of reading and writing data on disks?

A
  • Constant Linear Velocity (CLV)
  • Constant Angular Velocity (CAV)
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31
Q

The density of bits (bits/unit length) per track is uniform.

A

Constant Linear Velocity (CLV)

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32
Q

The outer tracks are longer with more bits than inner tracks, there are more sectors on the outer tracks.

A

Constant Linear Velocity (CLV)

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33
Q

The drive increases its rotation speed as the head from the outer to the inner tracks to keep the same rate of data moving the head.

A

Constant Linear Velocity (CLV)

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34
Q

This method is used in CD-ROM and DVD-ROM drives.

A

Constant Linear Velocity (CLV)

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35
Q

The number of bits per track is uniform (constant number of sectors).

A

Constant Angular Velocity (CAV)

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36
Q

This means that the density of bits per track increases from outer tracks to inner tracks.

A

Constant Angular Velocity (CAV)

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37
Q

This implies that the disk rotation stays constant.

A

Constant Angular Velocity (CAV)

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38
Q

This method is used in hard disks and floppy disks.

A

Constant Angular Velocity (CAV)

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39
Q

The time it takes to access a sector depends on:

A

(SLT)
- Seek Time
- Latency Time
- Transfer Time

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40
Q

It is the time it takes to move the read-write head to the correct track.

A

Seek Time

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41
Q

It is the time it takes for the sector to rotate under the head.

A

Latency Time

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42
Q

It is the time it takes to actually transfer data between disk and main memory.

A

Transfer Time

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43
Q

Aspects of Disk Management:

A
  • Disk Formatting
  • Boot Block
  • Bad Blocks
44
Q

Before a computer can make use of a new disk, the disk must be broken into the sectors that the computer can understand. What is this process called?

A

Physical Formatting

45
Q

When formatted, a disk consists of a set of sectors on each track the head can address.

A

Disk Formatting

46
Q

Each sector has a header containing the sector number and space for ____________.

A

Error Correcting Code (ECC)

47
Q

Each sector has a header containing the sector number and space for Error Correcting Code (ECC).

A

Disk Formatting

48
Q

This program initializes all aspects of the system, from CPU registers to device controllers to memory contents.

A

Bootstrap program

49
Q

The __________ program initializes all aspects of the system.

A

Bootstrap program

50
Q

Disks have moving parts and small tolerances so they are __________.

A

Prone to failure

51
Q

This means that the disk needs to be replaced or one or more blocks become unreadable and not writable.

A

Bad Blocks

52
Q

True or False
In Free Space Management, it is necessary to reuse space from deleted files for new files.

A

True

53
Q

To keep track of the free disk space, the system maintains a ____________.

A

Free-space list

54
Q

The four implementations of the free-space list are:

A
  • Bit Vector
  • Linked List
  • Grouping
  • Counting
55
Q

True or False
In Bit Vector, a single bit represents each block.

A

True

56
Q

True or False
If the block is free, the bit is 0; otherwise, the bit is 1.

A

True

57
Q

What is the main disadvantage of Bit Vector?

A

The bit map is kept in the main memory

58
Q

This approach is to link all the free disk blocks together, keeping a pointer to the first free block.

A

Linked List

59
Q

In Linked List, the approach is to link all the free disk blocks together, keeping a pointer to the ___________.

A

First free block

60
Q

This technique is not efficient because of the sequential nature of lists.

A

Link List

61
Q

In Grouping, a modification of the free-list approach is to store the _____________ in the first free block.

A

addresses of n free blocks

62
Q

True or False
In Grouping, the first n-1 is free.

A

True

63
Q

True or False
In Grouping, the last one is the address of another block with the addresses of another n free blocks.

A

True

64
Q

True or False
In Grouping, the addresses of a large number of free blocks can be found quickly.

A

True

65
Q

This approach is to consider that several contiguous blocks may be allocated or freed simultaneously.

A

Counting

66
Q

True or False
In Counting, rather thank keeping a list, the system keeps the address of the first free block and the number of free contiguous blocks that follow the first block.

A

True

67
Q

In Counting, each entry in the free-space list consists of ____________.

A

A disk address and a count

68
Q

What are the Allocation Methods:

A

(LIC)
- Linked-List Allocation
- Indexed Allocation
- Contiguous Allocation

69
Q

This allocation method requires each file to occupy a set of contiguous addresses in the disk.

A

Contiguous Allocation

70
Q

True or False
In Contiguous Allocation, if the file is “n” blocks long, starts at location “b”, it occupies blocks b, b+1, b+2, …, b + n - 1.

A

True

71
Q

In Contiguous Allocation, the ___________ indicates the address of the starting block (b) and the length of the area allocated for this file (n).

A

Directory Entry

72
Q

True or False
In Linked-List allocation, each files is a linked list of disk blocks; these may be scattered anywhere on the disk.

A

True

73
Q

In Linked-List allocation, the ________ contains a pointer to the first and last blocks of the file. Each block contains a pointer to the next block.

A

Directory

74
Q

True or False
In Linked-List allocation, there is no external fragmentation.

A

True

75
Q

In Linked-List allocation, any free block on the free-space list can be used to _________.

A

Satisfy a request.

76
Q

True or False
In Linked-List allocation, a file can continue to grow as long as there are free blocks.

A

True

77
Q

True or False
A disadvantage of Linked-List allocation is that pointers also occupy disk space.

A

True

78
Q

A variation of Linked-List allocation is the use of ___________.

A

File-Allocation Table (FAT)

79
Q

This table has one entry for each disk block and is indexed by block number.

A

File-Allocation Table (FAT)

80
Q

This allocation is similar to Linked-List allocation except the pointers to the blocks are not scattered but are grouped in one location which is the index block.

A

Indexed Allocation

81
Q

In Indexed allocation, each file has its own index block, which is an array of ___________ addresses.

A

Diskblock addresses

82
Q

Indexed allocation supports direct access, without suffering from ________________.

A

External fragmentation

83
Q

In Indexed allocation, the _____________________ is greater than the Linked-List allocation.

A

Pointer overhead

84
Q

True or False
In Indexed allocation, the OS must allocate an entire index block, even if one or two pointers will be non-nil.

A

True

85
Q

True or False
The OS can improve on the average disk service time by scheduling the requests for disk access.

A

True

86
Q

In Disk Scheduling, if the desired disk drive and controller are __________, it can service that request immediately.

A

Available

87
Q

In Disk Scheduling, if the drive or controller is serving on request, any additional requests, normally from other processes, should go to a ________.

A

Queue

88
Q

What are the Disk Scheduling Algorithms:

A
  • First-come First-served (FCFS) Scheduling
  • Shortest Seek Time First (SSTF) Scheduling
  • SCAN Scheduling
  • C-SCAN Scheduling
  • LOOK Scheduling
  • C-LOOK Scheduling
89
Q

This is the simplest form of scheduling.

A

FCFS Scheduling

90
Q

This scheduling selects the request with the minimum seek time from the current head.

A

SSTF Scheduling

91
Q

In SSTF Scheduling, the system moves the head to the __________________ in the request queue.

A

Closest Track

92
Q

The problem with SSTF Scheduling is that it may cause _________ of some requests.

A

Starvation

93
Q

True or False
In theory, SSTF Scheduling can have a continual stream of requests near one another could arrive, causing the request for a farther track to wait indefinitely.

A

True

94
Q

The _________ algorithm, although a substantial improvement over the FCFS algorithm, is not optimal.

A

SSTF Algorithm

95
Q

In _______ scheduling, the read-write head starts at one end of the disk, servicing requests as it reaches each track, until it gets to the other end.

A

SCAN Scheduling

96
Q

In SCAN scheduling, the direction of head movement reverses and servicing _______________, at the other end.

A

Continues

97
Q

It is also called the elevator algorithm, since it is similar to the behavior of elevators as they service requests to move from floor to floor.

A

SCAN Scheduling

98
Q

This algorithm is a variant of SCAN scheduling.

A

Circular-SCAN (C-SCAN) Scheduling

99
Q

This scheduling moves the head from one end of the disk to the other, servicing requests as it goes.

A

C-SCAN Scheduling

100
Q

When this scheduling reaches the other end, it immediately returns to the beginning of the disk without servicing the ones in a return trip/

A

C-SCAN Scheduling

101
Q

This scheduling treats the disk as though it were circular, with the last track adjacent to the first one.

A

C-SCAN Scheduling

102
Q

In these scheduling, the head always moves from one end of the disk to the other.

A

SCAN and C-SCAN Scheduling

103
Q

In these scheduling, the head only moves as far as the last request in each direction.

A

LOOK and C-LOOK Scheduling

104
Q

These scheduling are more appropriate for systems that place a heavy load on the disk.

A

SCAN and C-SCAN Scheduling

105
Q

If the queue sometimes has more than one outstanding request, then all scheduling algorithms are effectively equivalent. In this case, ____________ scheduling is a reasonable algorithm due to its simplicity.

A

FCFS Scheduling

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