Module 5 Flashcards
A system that has several disk platters made of metal or glass with a flat circular shape.
Magnetic Disk System
Where is the information stored in a magnetic disk?
In a magnetic recording material covering the two surfaces.
The disk surface is divided into ________ then subdivided into ________.
divided into TRACKS then subdivided into SECTORS
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.
True
What is the typical rotation speed of hard disks?
4500 to 7500 rpm.
True or False
In a hard disk, the faster the disk rotation, the higher the transfer rate.
True
True or False
If a hard disk rotates faster, it also becomes louder and hotter.
True
True or False
Modern hard disks read all sectors of a track in one turn (Interleave 1:1)
True
In modern hard disks, the rotation speed is _______.
Constant
It is when the head contacts the disk surface, scraping the recording medium off the disk, destroying data.
Head crashes
It is one of the earliest secondary-storage media.
Magnetic Tape
It was too slow compared with the access time of main memory and slower than disks.
Magnetic Tape
It is currently used mainly for backup, rarely useful information, and for transferring information.
Magnetic Tape
It provides the bulk of secondary storage for modern computers.
Magnetic Disks
In a magnetic disk, information is recorded ______________ on the sector under the read-write head.
Magnetically
A __________ system has a separate read-write head for each track.
Fixed-head system
This system allows the computer to switch from track to track quickly/
Fixed-head system
This system requires a large number of heads, making it expensive.
Fixed-head system
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).
Moveable-head system
All the tracks on one drive that can be accessed without moving the heads are called a _______.
Cylinder
____________ are coated with a hard surface, so the read-write head scans it directly on the disk surface without destroying the data.
Floppy Disks
One of the most commonly used floppy diskettes capable of storing 1.44 MB of data.
3.5” floppy diskette
How much data can a 3.5” floppy diskette store?
1.44 MB
A disk normally has a _________ indicating which files are on the disk.
Device directory
The directory lists the file by ________, and includes necessary information.
Name
The system stores the disk directory on the device, often at some ________.
Fixed disk address
Modern disks are addressed as ______________________ of logical blocks, the smallest unit of transfer, typically 512 bytes.
Large one-dimensional arrays
In modern disks, what is the smallest unit of transfer?
512 bytes
Some disks can be _________________ to choose another size such as 1024 bytes.
Low-level formatted
What are the two ways of reading and writing data on disks?
- Constant Linear Velocity (CLV)
- Constant Angular Velocity (CAV)
The density of bits (bits/unit length) per track is uniform.
Constant Linear Velocity (CLV)
The outer tracks are longer with more bits than inner tracks, there are more sectors on the outer tracks.
Constant Linear Velocity (CLV)
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.
Constant Linear Velocity (CLV)
This method is used in CD-ROM and DVD-ROM drives.
Constant Linear Velocity (CLV)
The number of bits per track is uniform (constant number of sectors).
Constant Angular Velocity (CAV)
This means that the density of bits per track increases from outer tracks to inner tracks.
Constant Angular Velocity (CAV)
This implies that the disk rotation stays constant.
Constant Angular Velocity (CAV)
This method is used in hard disks and floppy disks.
Constant Angular Velocity (CAV)
The time it takes to access a sector depends on:
(SLT)
- Seek Time
- Latency Time
- Transfer Time
It is the time it takes to move the read-write head to the correct track.
Seek Time
It is the time it takes for the sector to rotate under the head.
Latency Time
It is the time it takes to actually transfer data between disk and main memory.
Transfer Time
Aspects of Disk Management:
- Disk Formatting
- Boot Block
- Bad Blocks
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?
Physical Formatting
When formatted, a disk consists of a set of sectors on each track the head can address.
Disk Formatting
Each sector has a header containing the sector number and space for ____________.
Error Correcting Code (ECC)
Each sector has a header containing the sector number and space for Error Correcting Code (ECC).
Disk Formatting
This program initializes all aspects of the system, from CPU registers to device controllers to memory contents.
Bootstrap program
The __________ program initializes all aspects of the system.
Bootstrap program
Disks have moving parts and small tolerances so they are __________.
Prone to failure
This means that the disk needs to be replaced or one or more blocks become unreadable and not writable.
Bad Blocks
True or False
In Free Space Management, it is necessary to reuse space from deleted files for new files.
True
To keep track of the free disk space, the system maintains a ____________.
Free-space list
The four implementations of the free-space list are:
- Bit Vector
- Linked List
- Grouping
- Counting
True or False
In Bit Vector, a single bit represents each block.
True
True or False
If the block is free, the bit is 0; otherwise, the bit is 1.
True
What is the main disadvantage of Bit Vector?
The bit map is kept in the main memory
This approach is to link all the free disk blocks together, keeping a pointer to the first free block.
Linked List
In Linked List, the approach is to link all the free disk blocks together, keeping a pointer to the ___________.
First free block
This technique is not efficient because of the sequential nature of lists.
Link List
In Grouping, a modification of the free-list approach is to store the _____________ in the first free block.
addresses of n free blocks
True or False
In Grouping, the first n-1 is free.
True
True or False
In Grouping, the last one is the address of another block with the addresses of another n free blocks.
True
True or False
In Grouping, the addresses of a large number of free blocks can be found quickly.
True
This approach is to consider that several contiguous blocks may be allocated or freed simultaneously.
Counting
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.
True
In Counting, each entry in the free-space list consists of ____________.
A disk address and a count
What are the Allocation Methods:
(LIC)
- Linked-List Allocation
- Indexed Allocation
- Contiguous Allocation
This allocation method requires each file to occupy a set of contiguous addresses in the disk.
Contiguous Allocation
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.
True
In Contiguous Allocation, the ___________ indicates the address of the starting block (b) and the length of the area allocated for this file (n).
Directory Entry
True or False
In Linked-List allocation, each files is a linked list of disk blocks; these may be scattered anywhere on the disk.
True
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.
Directory
True or False
In Linked-List allocation, there is no external fragmentation.
True
In Linked-List allocation, any free block on the free-space list can be used to _________.
Satisfy a request.
True or False
In Linked-List allocation, a file can continue to grow as long as there are free blocks.
True
True or False
A disadvantage of Linked-List allocation is that pointers also occupy disk space.
True
A variation of Linked-List allocation is the use of ___________.
File-Allocation Table (FAT)
This table has one entry for each disk block and is indexed by block number.
File-Allocation Table (FAT)
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.
Indexed Allocation
In Indexed allocation, each file has its own index block, which is an array of ___________ addresses.
Diskblock addresses
Indexed allocation supports direct access, without suffering from ________________.
External fragmentation
In Indexed allocation, the _____________________ is greater than the Linked-List allocation.
Pointer overhead
True or False
In Indexed allocation, the OS must allocate an entire index block, even if one or two pointers will be non-nil.
True
True or False
The OS can improve on the average disk service time by scheduling the requests for disk access.
True
In Disk Scheduling, if the desired disk drive and controller are __________, it can service that request immediately.
Available
In Disk Scheduling, if the drive or controller is serving on request, any additional requests, normally from other processes, should go to a ________.
Queue
What are the Disk Scheduling Algorithms:
- First-come First-served (FCFS) Scheduling
- Shortest Seek Time First (SSTF) Scheduling
- SCAN Scheduling
- C-SCAN Scheduling
- LOOK Scheduling
- C-LOOK Scheduling
This is the simplest form of scheduling.
FCFS Scheduling
This scheduling selects the request with the minimum seek time from the current head.
SSTF Scheduling
In SSTF Scheduling, the system moves the head to the __________________ in the request queue.
Closest Track
The problem with SSTF Scheduling is that it may cause _________ of some requests.
Starvation
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.
True
The _________ algorithm, although a substantial improvement over the FCFS algorithm, is not optimal.
SSTF Algorithm
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.
SCAN Scheduling
In SCAN scheduling, the direction of head movement reverses and servicing _______________, at the other end.
Continues
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.
SCAN Scheduling
This algorithm is a variant of SCAN scheduling.
Circular-SCAN (C-SCAN) Scheduling
This scheduling moves the head from one end of the disk to the other, servicing requests as it goes.
C-SCAN Scheduling
When this scheduling reaches the other end, it immediately returns to the beginning of the disk without servicing the ones in a return trip/
C-SCAN Scheduling
This scheduling treats the disk as though it were circular, with the last track adjacent to the first one.
C-SCAN Scheduling
In these scheduling, the head always moves from one end of the disk to the other.
SCAN and C-SCAN Scheduling
In these scheduling, the head only moves as far as the last request in each direction.
LOOK and C-LOOK Scheduling
These scheduling are more appropriate for systems that place a heavy load on the disk.
SCAN and C-SCAN Scheduling
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.
FCFS Scheduling
